When I first received this question I must confess I thought it was a really silly question... C'mon, how in the earth would someone not know what IT is?
However, after reading the question, I became aware that it could really help a lot of people because I see a lot of developers making some confusion with this.
Basically, the most basic definition for IT is: "Set of tools, processes, and methodologies (such as coding/programming, data communications, data conversion, storage and retrieval, systems analysis and design, systems control) and associated equipment employed to collect, process, and present information. In broad terms, IT also includes office automation, multimedia, and telecommunications." (Source: http://www.businessdictionary.com/definition/information-technology-IT.html)
I find this definition to be exclusive and I must tell you why...
Wanna know more? Watch this video and find out!