A lipogram (from Ancient Greek: λειπογράμματος, leipográmmatos, "leaving out a letter") is a kind of constrained writing or word game consisting in writing paragraphs or longer works in which a particular letter or group of letters is avoided—usually a common vowel, and frequently "E", the most common letter in the English language.
A univocalic is a type of lipogrammatic constrained writing that uses only a single vowel, "A", "E", "I", "O", or "U", and no others - the Wikipedia page is .
A pangrammatic lipogram is a text that uses every letter of the alphabet except one. For example, "The quick brown fox jumped over the lazy dog" omits the letter S, which the usual pangram includes by using the word jumps.
More information on the Wikipedia page .
There are a number of other websites, eg .