Analytics tools like Google Analytics can automatically detecting some things about your incoming traffic (for example, that they came from a search engine, or a previous website.) However, this information is fairly rudimentary. Therefore, analytics solutions provide a way for you to TELL them how the traffic is getting there. For GA, this is utm (aka campaign) tracking. You can read about GA's solution here: http://bit.ly/ga-url-builder (Link 1)

The most important thing is that your marketers are consistent. (For example, that they all use "social" as the Medium - not "socialmedia" or "sm" or "social" - these will lead to multiple Mediums that all mean the same thing!) So whatever you choose to name things, keep them used consistently.

A shared spreadsheet like this one can be a helpful start. You can add drop downs and data validation to force even more consistency! Just make a copy, and customise to your heart's content. http://bit.ly/ga-url-builder-sheet (Link 1)

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