Indefinite and fictitious numbers are words, phrases and quantities used to describe an indefinite size, used for comic effect, for exaggeration, as placeholder names, or when precision is unnecessary or undesirable. Other descriptions of this concept include: "non-numerical vague quantifier" and "indefinite hyperbolic numerals".

Umpteen, umteen or umpty is an unspecified but large number, 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 seem to indicate that it lies between 12 and 20, umpteen can be much larger.

The oldest reference to "umpty" — in a June 17, 1848 issue of the Louisville Morning Courier — indicates that at that time it was slang for empty. This is confirmed by a humorous short story in the North Carolina Hillsborough Recorder of June 30, 1852.

By 1905, "umpty", in the expression "umpty-seven", had come to imply a multiple of ten. Umpty came from a verbalization of a dash in Morse code.

"Umpteen", adding the ending -teen, as in "thirteen", is first attested in 1884, and has become by far the most common form.

In Norwegian, ørten is used in a similar way, playing on the numbers from tretten (13) to nitten (19), but often signifying a much larger number.

Similarly, though with a larger base, Portuguese has milhentos, which is derived from the words mil(har) (1000) and the suffix -entos, present in words like trezentos (300) or quinhentos (500), roughly meaning "hundred".

Spanish uses tropecientos/tropecientas in Spain and chorrocientos/chorrocientas in El Salvador and Mexico referring to a high number in a colloquial way. Cientos means "hundreds".