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In everyday language: the quality of being unpaired, occasional, strange or unusual

In mathematics:

an integer is odd if dividing it by two does not result in another integer; see even and odd numbers

a function f defined on the real numbers is odd if f(x) = −f(−x) for all x; see even and odd functions

a permutation of a finite set is odd if it can be written as the composition of an odd number of transpositions; see even and odd permutations

In probability theory, the odds in favor of an event is the ratio of the event's probability to the complementary probability.

Odd, a name of Norse origin, the 10th most common male name in Norway (curiously, Even is also a common Norwegian name). In old norse the word means the sharp end of a weapon, e.g. edge of a sword or spear/arrow head.

Optical Disk Device

Oppositional Defiant Disorder

Odd, West Virginia, USA

Odd Grenland B.K., is a Norwegian football team

Odd Della Robbia, a character in Code Lyoko