Term
Side Out
Also called: Sideout
When the serve passes to the other team.
When the serving side loses the serve and it passes to the opponents (Section 2, Definitions). In singles, it is a side out when the server loses a rally (5.A.3). In doubles, it is a side out when both players have lost a rally. However, at the start of each game, the side that serves first has only one server (5.B, 5.B.6).
In rally scoring doubles, it is a side out as soon as the serving side loses one rally (14.A.5). For details, see The score call (three numbers).
See it in a figure
This figure is from the rule "Serving order in doubles".
How to read the sources: numbers like (8.F.4) are rulebook sections, and links are outside sources. An "Author's note" is the author's personal experience, not an official rule.