In stories, the Straight Man is the character who plays level headed pragmatist to an ever sillier or over the top cast of characters. These are characters who call fellow heroes, villains and pedestrians out on outlandish or nonsensical behavior. Alternatively, they are simply the voice of reason who try to settle conflicts between others. Straight Men often double as being genre savvy- which is noting cliche's so broadly formulaic that the very characters in the story can recognize them and even plan accordingly.
Contrary to the name, a Straight Man can be male or female.