I'm not in a team so i'm maybe not the best person to ask, but here is how I think about it:
It's whatever you want it to be.
Why should there be a strict definition? I think different teams have different goals.
One might be a loose organisation of racers who are not extremely ambitious but who like to race together on a public server or on their teamserver, exchanging knowledge, join a league or event every once in a while, etc. Some people like to be in a team but can't/don't want to deal with the "obligation" to reserve time for leagues and such.
And another team might be really ambitious and striving to be the best there is, joining lots of leagues and events and really going for the wins.