"+", ASCII character 43, 0x2B. The mathematical symbol for the addition operator, also used with the same meaning in arithmetic expressions in nearly all programming languages.
Common names: ITU-T: plus; add. Rare: cross; INTERCAL: intersection.
In programming, the operator is sometimes overloaded to perform other tasks like concatenating strings. In the C language and its many imitators, the symbol is doubled, as in "x++" or "++x" to give an increment operator that adds one to its operand ("x" in this case) and also returns x's previous or resulting value respectively.
In a regular expression, "+" means match one or more instances of the previous pattern. Thus /b(an)+a/ would match any of "bana", "banana", "bananana", etc. (see banana problem).