The opposite of even.

All integers are either even or odd, with numbers evenly distributed (and alternating) across both sets. A test to see if an integer is even or odd is whether or not said number is cleanly divisible by two (if so, the number is even, otherwise it is odd). In an exponent-based number system, this test can be reduced to looking at the last digit, and determining whether it is cleanly divisible by two, with the same test applied.

A common programming construct is to perform a bitwise AND with a number and a single 1 bit, the boolean result of which will tell whether the number in question is odd:

BOOL is_odd = test & 1;