Concatenation

In formal language theory (and therefore in programming languages), concatenation is the operation of joining two character strings end to end. For example, the strings "foo" and "bar" may be concatenated to give "foobar".

The Unix cat command concatenates files in a similar way.

Concatenation in Maths

Concatenation is the joining of two strings, that is, when a and b are concatenated, they form ab. Concatenation of two strings, a and b is denoted as ab or a||b.