An integer is a whole number that can be positive or negative. Integers are stored in computers using a fixed number of bits, determining the range of numbers that can be represented. Most computers use 32 bits to store integers in two's complement format, allowing values from approximately -2 billion to 2 billion. In two's complement, the most significant bit represents the sign, with 1 indicating negative and 0 positive, and negative numbers are calculated by inverting and adding 1 to the binary representation.