Medium Armor's looks depends on the game, but gives the player 25 armor points when picked up (however, it will not exceed past 100 armor points). In Serious Sam 1, Serious Sam HD and Serious Sam: Next Encounter, it is a harness with yellow stripes on it, a yellow chest plate in Serious Sam 2 and a bulletproof vest with a desert camouflage pattern in Serious Sam 3: BFE.
Medium Armor is most often found throughout levels as a common pickup item so that the player will have some armor. Some pieces of Medium Armor are booby trapped, so the player should be careful when picking up one that's far away.
A few Medium Armor suits can be found in secrets, but are always found among other items, like ammo. Medium Armor gives away too little armor points to be in a secret by itself.