There is a lot of confusion around anarchism, because it is a negative description: It's a collective without leader, without governing institutions. It doesn't say much about how this collective organizes instead. So you could call the chaotic state after a government coup Anarchy. But that isn't what anarchists are talking about and I don't think that is what OP meant either.

Anarchy as a deliberate system is when a group of people decides to work or live together without selecting a leader or any other form of government, instead resolving decisions that affect everyone together. In that sense it is not an interim state, a leadership-vacuum just waiting to be filled. Although of course Anarchy can transition into another system by various means, but so can every other system as well.