Meaning

• A submarine.

• A submarine sandwich: a sandwich made on a long bun.

  "We can get subs at that deli."

• A substitute, often in sports.

  "She worked as a sub until she got her teaching certificate."

• (often in plural) A subscription: a payment made for membership of a club, etc.

• A subtitle.

  "I've just noticed a mistake in the subs for this film."

• A subroutine (sometimes one that does not return a value, as distinguished from a function, which does).

• A subeditor.

• A subcontractor.

• (BDSM) A submissive.

• A subordinate.

• A subaltern.

• A subscription (or (by extension) a subscriber) to an online channel or feed.

  "I'm totally stoked; just got 10 new subs after my last video."

• Subsistence money: part of a worker's wages paid before the work is finished.

Meaning

• To substitute for.

• To work as a substitute teacher, especially in primary and secondary education.

• To replace (a player) with a substitute.

  "He never really made a contribution to the match, so it was no surprise when he was subbed at half time."

• Less commonly, and often as sub on, to bring on (a player) as a substitute.

  "He was subbed on half way through the second half, and scored within minutes."

• To perform the work of a subeditor or copy editor; to subedit.

• To lend.

• To subscribe.

• (BDSM) To take a submissive role.