Proper differentiation between IT(information technology), CS(Computer Science) and SE(Software Engineering) is important for anyone who studies or is willing to study one of these fields. Each one of them leads to a completely different path (as one is completely different area of study to begin with), amazingly there are very few Instructors at universities who can clearly differentiate one from the other.

Lets begin with the first one:

IT (Information Technology):

IT deals with input, manipulation and output of data, for example: a student information system in a university. In other words its engineering every aspect of data, its storage, processing and retrieval.

CS (Computer Science):

Deals with theories and research on how computers work (both software/hardware) at a very low level. A Computer scientist may deal with research on data structures or algorithms and present a better data structure or algorithm in a specific scenario, but he will never be concerned with the development of complex computer software. In other words, computer scientist give us number of choices in terms of laws, theories, complexity of certain algorithms (just like laws in mathematics or physics that we later use in large scale projects).

SE (Software Engineering):

Deals with all aspects of the development of a complex computer software, while complex means, teams than one developer, software for some corporation than for yourself or a prototype, software conforms to the requirements of the client or stake holders than yourself and one that has huge consequences in terms of cost or risks. To engineer a computer software in such an environment is what its really like to be a software engineer.