Actually, it was just a joke... and since the explanation is sort of interesting, I'll go into it.

Take the equation of this general form, rendered here in Perl:

($x**$n + $y**$n) == $z**$n;

The Pythagorean Theorem, which you doubtless remember, involves a special case:

($x**2 + $y**2) == $z**2;

In 1637, Pierre de Fermat claimed that the general equation was false for any case where ($n > 2); this became known as Fermat's Last Theorem. The theorem was proven only recently, in enormously complex fashion, after about 350 years of anguished mathmeticians losing sleep over it.

Which brings us to the joke. Fermat, in describing his theorem, noted, "I have discovered a truly marvellous proof, which this margin is too narrow to contain." Which is fairly ridiculous; he pretty certainly discovered no such thing. And neither have I.