Unary Operation

An operation that has only one input.

Example: the square root function.
√(16) = 4 has just one input "16" to produce an output of "4"

There are many more: factorial, sine, cosine, etc. are all unary operations.

Note: a "binary operation" has two inputs.
Example: the plus operation is a binary operation: 3+5 has two inputs ("3" and "5") to produce an output of "8"