General definitions of 'discourse' can be 'verbal interchange of ideas' or 'formal and orderly and usually extended expression of thought on a subject.' Different fields have more specific definitions, though.
A 'discourse' is a discussion about a topic. Usually a discourse involves more than a group of people talking; a discourse would normally include people giving reasons for the opinions being expressed in the conversation. The speakers might be giving evidence for why they are expressing the ideas they are sharing. The ideas and the information supporting those ideas are probably coming from some sort of media, whether it be internet, social networking media, television, or some other form of communication. The media allow the speakers to have a more detailed conversation, or discourse.
Discourse can simly be defined as conversations between people. When we interact with each other using verbal communication, we are having a discourse.
Discourse depend on media primarily because of the strong cultural influence of the later. Pop culture such as music, films, sports, TV shows, etc--all those things which people see in different forms of media are creating a great impact in the the audiences' way of life.
We must remember that culture and language can never be separated, they co-exist, if one dies, the other dies too. Currently, we know that media is becoming more and more influencial in human culture. We model many of our ways and toughts from what we see in media. We are convinced to buy different brands and products through ads, we imitate the clothing fasion of movie stars, we patern our life style on famous personalities, we abide by the principles of influencial people--and all our access to these are provided by media.
The primary tool of media, aside from technology which allows it to reach us is the language-language that directly and impliedly influence and affect the language of people who normally pattern their discourse model from what they see on media.