Short-term memory (sometimes referred to as "primary memory" or "active memory") refers to the capacity for holding a small amount of information in mind in an active, readily available state for a short period of time. The duration of short-term memory (when rehearsal or active maintenance is prevented) is believed to be in the order of seconds. Estimates of short-term memory capacity limits vary from about 4 to about 9 items, depending upon the experimental design used to estimate capacity. A commonly-cited capacity is 7±2 elements. In contrast, long-term memory indefinitely stores a seemingly unlimited amount of information.

Short-term memory should be distinguished from working memory which refers to structures and processes used for temporarily storing and manipulating information (see more details below).