A career in Information Systems involves design, installation and maintenance of computer-based business information systems. Information systems managers direct the work of systems analysts, computer programmers, support specialists, and other computer-related workers. These managers plan and coordinate activities such as the installation and upgrading of hardware and software, programming and systems design, the development of computer networks, and the implementation of Internet and intranet sites. For example, working with their staff, they may develop the overall concepts of a new product or identify computer-related problems standing in the way of project completion.
Source: Occupational Outlook Handbook, Dept of Labor

An information system is a business application of the computer. It is made up of the database, application programs, manual and machine procedures and encompasses the computer systems that do the processing.

The database stores the subjects of the business (master files) and its activities (transaction files). The application programs provide the data entry, updating, query and report processing. The manual procedures document how data are obtained for input and how the system's output is distributed. Machine procedures instruct the computer how to perform the batch processing activities, in which the output of one program is automatically fed into another program.

Source: Techweb

Processing information by computer. The term usually embraces the computer hardware, computer software, and storage technology used by a company's processing systems. Communications technology (hardware and software) and networks link the pieces together, and allow the company to share information. The combination of all these technology resources is frequently called an information technology infrastructure, or platform. A successful company must build and maintain an information technology infrastructure in order to develop effective information systems.

Alternate definition for IT:
The latest title for the information processing industry. There have been several before it. IT as an umbrella term for information processing became popular in the 1990's. The term may embrace or exclude the telecom industry, depending on whom you talk to.

Source: Techweb

An information system is a computer-based business system that uses information technology to store, manipulate and display business information. Information systems are generally designed to interact with or support other business systems and are a key factor in analysis and decision-making by management.

Information Technology is the hardware and software used by information systems. A successful company must build and maintain an information technology infrastructure, comprised of hardware, software, storage and communication technologies, in order to develop effective information systems.

Management of information systems (MIS) involves information systems and computing resources for entire organizations. MIS directors work under the chief information officer and manage a staff of information technology employees. Management of information systems directors plan, coordinate, and direct research and design the computer-related activities of firms. They determine technical goals in consultation with top management, and make detailed plans for the accomplishment of these goals. MIS directors may also make hardware and software upgrade recommendations based on their experience with an organization's technology.
Source: Occupational Outlook Handbook, Dept of Labor

The study of management information systems focuses on how information systems are used by a business, and how management can integrate systems across departments. An MIS program combines theoretical areas like management science and computer science with practical coursework in applications software and information system design.

An information system that integrates data from all the departments it serves and provides operations and management with the information they require. Factors involved in a management system include an organization's goals and objectives, strategies and tactics, plans, schedules and controls.

Source: Techweb

Computer software engineers apply the principles and techniques of computer science, engineering, and mathematical analysis to the design, development, testing, and evaluation of the software and systems that enable computers to perform their many applications.

Software engineers can be involved in the design and development of many types of software:

• Computer applications software engineers analyze users' needs and design, create, and modify general computer applications software or specialized utility programs. Different programming languages are used, depending on the purpose of the program.
• Computer systems software engineers coordinate the construction and maintenance of a company's computer systems, and plan their future growth. Working with a company, they coordinate each department's computer needs and make suggestions about its technical direction.

Computer programmers write, test, and maintain the detailed instructions, called programs, which computers must follow to perform their functions. They also conceive, design, and test logical structures for solving problems by computer.

Programmers write programs according to the specifications determined primarily by computer software engineers and system analysts. After the design process is complete, it is the job of the programmer to convert that design into a logical series of instructions that the computer can follow. They then code these instructions in programming language, such as COBOL, Prolog, Java, C++, or Smalltalk. Different programming languages are used depending on the purpose of the program.

Many programmers update, repair, modify, and expand existing programs. When making changes to a section of code, called a routine, programmers need to make other users aware of the task the routine is to perform.

Programmers test a program by running it, to ensure the instructions are correct and it produces the desired information. If errors do occur, the programmer must make the appropriate change and recheck the program until it produces the correct results. This process is called debugging.

Source: Occupational Outlook Handbook, Dept of Labor

Software engineers must possess strong programming skills, but are more concerned with developing algorithms and analyzing and solving programming problems than with actually writing code.

Computer programmers write programs according to the specifications determined primarily by computer software engineers and system analysts. After the design process is complete, it is the job of the programmer to convert that design into a logical series of instructions that the computer can follow. They then code these instructions in the appropriate programming language.

Computer Science
Computer scientists work as theorists, researchers, or inventors. Their jobs are distinguished by the higher level of theoretical expertise and innovation they apply to complex problems and the creation or application of new technology. Those employed by academic institutions work in areas ranging from complexity theory, to hardware, to programming language design. Some work on multi-disciplinary projects, such as developing and advancing uses of virtual reality, in human-computer interaction, or in robotics. Their counterparts in private industry work in areas such as applying theory, developing specialized languages or information technologies, or designing programming tools, knowledge-based systems, or even computer games.
Source: Occupational Outlook Handbook, Dept of Labor

Systems analysts
Systems analysts solve computer problems and enable computer technology to meet individual needs of an organization. They plan and develop new computer systems or devise ways to apply existing systems' resources to additional operations. Most systems analysts work with a specific type of system that varies with the type of organization they work for-for example, business, accounting, or financial systems, or scientific and engineering systems.

Analysts begin an assignment by discussing the systems problem with managers and users to determine its exact nature. They define the goals of the system and divide the solutions into individual steps and separate procedures. Analysts use techniques such as structured analysis, data modeling, information engineering, mathematical model building, sampling, and cost accounting to plan the system.

Source: Occupational Outlook Handbook, Dept of Labor