In electronics (specifically, signal processing), half time usually refers to the time it takes for the amplitude of a pulse to drop from 100% to 50% of its peak value.

$t\_\{half\};=;t\_2;-;t\_1,!$

In some team sports such as football (soccer) and rugby, matches are played in two halves. Half-time (also written halftime or half time) is the name given to the interval between the two halves of the match. Typically, after half-time teams swap ends of the field of play, in order to reduce any advantage that may be gained from wind or a slope to the pitch, for example. While it exists mainly to provide competitiors to rest briefly and recover from the play of the first half, half-time also serves a number of other purposes.

One early use of half-time, and it is suggested the origin of the practice, was to allow for two football teams each used to a different set of rules to play half of the game by familiar rules, and half by the opposition rules. This was practised notably between followers of Eton rules football (closer to modern association football) and Rugby rules football (closer to modern rugby http://en.wikipedia.org/wiki/Rugby_union). This use of half-time was unnecessary after the standardisation of football rules in 1863 http://en.wikipedia.org/wiki/Laws_of_Football#History_and_development.