What is type check validation?

A type check validation validates whether or not the data you typed in a field on a web form is actually of the type of field it is. For example, this check won't let you type in "four thousand" in a number box, but will let you type in 4,000. It will also stop you from entering incorrect dates, like 13/13/11 or 31/02/97 (there aren't 31 days in February!)