A cloze test is a special type of gap fill exercise where, for example, every 5th word in a paragraph of about 150 words is deleted. (It could be every 6th word, or every 7th word, and so on.)
Cloze tests are a very good indicator of general ability in the language: usually a student who gets a good score in a cloze text is a good “all-rounder” in the language.
See also gap fill exercise.