In cooking, a pinch is a very small amount of an ingredient, typically salt or spice. Since it is defined as the amount that can be held between the thumb and index finger, the exact amount varies between persons and ingredients.
Pinch hitters are used principally in two situations: to replace a weak hitter (often the pitcher, although a weak-hitting defensive specialist can also be a target), or to gain a platoon advantage.
A pinch hitter may be substituted by another pinch hitter before his turn at bat is completed, for example if the opposing manager reacts to the pinch hitter's announcement by changing his pitcher.
A number of pitchers have also been used as pinch hitters; this tactic had almost disappeared by the 1980's, but is enjoying a limited revival of late, because major league benches have shrunk, with most managers having 12 or 13 pitchers on their 25-man roster, leaving few options for pinch hitting.