UmpteenUmpteen is a slang term for an unspecified number, generally used in a humorous fashion or to imply that it is not worth the effort to pin down the actual figure.
Despite the -teen ending, which would indicate that it lies between 12 and 20, umpteen is often assumed be much larger than this - if it could ever be pinned down. It is unclear where the ump portion of the word came from, but one theory is that it could have arisen from a sound used by speakers to indicate uncertainty. A derived term using the same root is umpty-ump.
A number of other slang terms exist to connotate even larger, but equally uncertain, numbers. Most are constructed by placing a nonsense syllable before the suffix -illion - e.g., gazillion.