Lexeme is a term in linguistics. They are units of meaning, independent of any inflectional endings, or whether it is one word or several. "Come in" is a lexeme; so is "raining cats and dogs". The largest English dictionaries have about half a million lexemes. "The true figure is undoubtedly a great deal higher".

In the English language, run, runs, ran and running are forms of the same lexeme, conventionally written as RUN.