What is the checked keyword in C#?

The checked keyword is used to control the overflow-checking context for integral-type arithmetic operations and conversions. It can be used as an operator or a statement according to the following forms.
The checked statement:

checked block

The checked operator:

checked (expression)

where:

block

The statement block that contains the expressions to be evaluated in a checked context.

expression

The expression to be evaluated in a checked context. Notice that the expression must be in parentheses ( ).