Friend is a four letter word meaning

What does the expression friend is a four letter word mean
So when John McCrea says "friendisafourletterword," I think that he is really saying that the word 'friend' has lost it's meaning. Just look at all the facebook and myspace junkies out there. It could also be interpreted as a friendship gone sour. The next line of the cake song states "End is the only part.

CAKE - Friend Is a Four Letter Word Lyrics - Lyreka
Most of my friendswere listening to early Britney or the Spice Girls at the time but my dad had me and my sisters listening to this "weird music." The meaning is pretty obviously about betrayal from a friend, that 'friend' becomes afourletterword, AKA a curse word. Despite the sparse lyrics, they're quite.