A heterogram (from hetero-, meaning "different", + -gram, meaning "written") is a word, phrase, or sentence in which no letter of the alphabet occurs more than once.
An isogram, in which all letters occur an equal number of times, is the same as a heterogram when each letter occurs once.
A heterogram may be distinguished from a pangram (a holoalphabetic sentence), which uses all of the letters of the alphabet (possibly more than once). A perfect heterogram is, however, the same as a perfect pangram, since both consist of all letters of the alphabet with each represented exactly once.
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