Im not sure if there is a definitions page but primary and secondary refer to the fermenters or the steps that are used in two stage fermentation. First you ferment in your primary and then you go to the secondary after getting identical readings with your hydrometer 3 days in a row.
However most people leave their beer in a primary for the majority if not ALL of the time they ferment, which should be at least 3 weeks. People mostly use secondaries for clearing out their beer or adding fruit.
Primary is exactly that. The first place your beer and or wine will live. Please train your brain to think "Clearing Tank" when you read Secondary. Most of us (Beer only) have pretty well abandoned the secondary or clearing stage of fermentation, because the beer will clear in the primary fermentor just fine, and will also benefit from having the yeast present to clean up some of the undesirable flavors that it may produce.