Learn in the textbookFundamentals of Interface Design and Input Operations
DefinitionMulti-touch interface (マルチタッチインタフェース) is an input method that detects contact at several points on the screen at the same time and lets you operate by combining them.
ExplanationA pinch out (ピンチアウト), which spreads two fingers to zoom in, and a pinch in (ピンチイン), which brings them together to zoom out, work only because several contact points can be handled at once. A method that detects just one contact point cannot perform such gestures.
AnalogyLike a pianist pressing keys with fingers of both hands at once to play a chord, it combines the movements of several fingers to convey one meaning.
Memory hookMulti means many or several. It is the same prefix as in multimedia, and here it means there are several touch points.