Term
Second Server
Also called: Server 2
In doubles, the player who serves second. Their server number is "2".
In doubles, the partner of the first server. They serve after the first server loses the serve (Section 2, Definitions, 5.B.5). The third number in the score call is "2" (6.B.2).
When the second server also loses a rally, it is a side out (5.B.6). At the start of each game, only the player who serves first on the serving side serves, as the second server, so the game starts at "0-0-2" (5.B, 5.B.2, 6.B.2, Serving order in doubles).
In rally scoring doubles, only one player per team serves until a side out (14.A.5).
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.