The Collaborative International Dictionary
Alla breve \Al`la bre"ve\ [It., according to the breve.] (Old Church Music) With one breve, or four minims, to measure, and sung faster like four crotchets; in quick common time; -- indicated in the time signature by ?. [1913 Webster] ||
Wiktionary
n. (context music English) a time signature when the half note is the beat and there are two beats per measure
WordNet
n. a musical time signature indicating two or four half notes to a measure
Wikipedia
Alla breve is a musical meter notated by the time signature symbol (a C with a line through it), which is the equivalent of . The term is Italian for "in the style of the breve".
Alla breve is a " simple- duple meter with a half-note pulse". The note denomination which represents one beat in is the minim or half-note. There are two of these per bar, so that the time signature may be interpreted as "two minim beats per bar."
In Italian, breve means short (for a period of time), and alla breve is also known as cut time or cut common time. (Common time, notated with the time signature symbol , is the equivalent of . It uses a quarter note (or crotchet) beat and there are four per bar.)