From entry short-term memory in glossary Human Computer Interaction the Basics
Short-term or working memory is the part of human memory that keeps track of the things you are currently doing, such as where you are in a sentence or the numbers you are adding up in your head. It operates for a limited time, usually just tens of seconds or a minute unless rehearsed, that is when it is used or you repeat things to yourself. It also has a limited capacity of "seven plus or minus 2" chunks, although a 'chunk' can be quite big, something for which you already have a representation in your long-term memory, such as "my childhood friend's house number".