Characters in Japanese anime often say, "Are you an S or an M?" What does this mean? What does s mean? What does M stand for?

S stands for attack, and M stands for answer: (see below)

Attack: BL(boylove) as the active party, that is, the number one among gay men. The antonym of "attack" is "acceptance", and acceptance is zero.

The following year's attack: the attack age is younger than the receiving age.

Annual attack: attack is better than attack.

Shroud Queen: Shrouds are as arrogant as queens, and can eat attacks to death.

Chivalrous Xia Shang: The low position is attack, and the high position is reception.

Position reversal: attack each other and accept each other's change of identity.

Always accept: No matter who you partner with, you are playing a receiver.

General attack: No matter who you are paired with, you are acting as an attack.

Strong air raid: an attack with strong personality.

A cocktail party with strong atmosphere: a cocktail party with strong personality.

Righteousness reception: a lively, healthy and cheerful reception.

Natural acceptance: less personality acceptance.

Temptation: active temptation and self-acceptance.

Abdominal black reception: the surface is reception, and the heart is attack.