This number is probably the most recognisable integer in all of geekdom - all thanks to Douglas Adams.

But 42, as well as being the answer to the meaning of life is also the ASCII for '*' - which, aptly, is used as the wildcard symbol meaning 'everything'

(It's also 6 x 9 in base 13, XLII in roman numerals, and 101010 in binary, but all are less significant)