A competition is one athlete's participation in a real race — an entry on their training calendar, just like a workout plan or a note. It links to a shared race event (the Berlin Marathon, your club time trial…), and carries everything specific to that one athlete: the day they race it, their goal, and — once it is over — their result.
When you record a session on your watch (Garmin, Coros, Suunto, Wahoo, Polar, Apple Watch, Rouvy, Strava…) and it syncs to Good Coach App, the app tries to put it in the right place on your calendar:
The Races screen is a shared, cross-club catalogue of real race events — the Berlin Marathon, your club time trial, a local 10K. A single race event is entered once and is then reused by everyone: every athlete who takes part links their own competition to that same shared race, so results from different clubs line up side by side on one page.