Winning a rally while the other team serves: you take the serve back — and indoors the whole team rotates one position onward.
Side-out is the basic unit of volleyball now that rally-point scoring hands out a point on every exchange. It used to be that only the serving team could score, so a side-out simply won you the ball back; today it delivers a point, the serve and the rotation in one go. That is exactly why side-out percentage is the most honest team stat you can keep: it measures how reliably you turn the opponent's serve into your own point — and it hangs on your passing, not on a spectacular attack. The common thinking error is watching only aces and block points. Both are rare, and a block point comes on roughly 10% of attacks; a side-out chance, by contrast, arrives with every single serve the other team hits. One detail that catches switchers out: the same logic applies in the sand, only without rotation — with two players it is just the serving order that changes.