Instead of using a weapon to make a melee weapon attack, you can use an unarmed strike: a punch, kick, head-butt, or similar forceful blow (none of which count as weapons). Although an unarmed strike is not a weapon, you can use an unarmed strike to make a melee weapon attack.

Are unarmed strikes martial weapons?

Unarmed strike are not considered a "melee-weapon" attacks, it is considered a melee "weapon-attack" since the PHB errata fixed that issue and removed the unarmed strike from the melee-weapon's list.

Is unarmed strike a weapon Pathfinder?

An unarmed strike is always considered a light weapon. ... A monk or any character with the Improved Unarmed Strike feat can deal lethal or nonlethal damage with unarmed strikes, at his discretion. Pathfinder RPG Core Rulebook.