The terms "X-wing" and "Y-wing" and "TIE fighter" were used by ILM effects guys to distinguish the fighters. These terms are not used in this film, though they were incorporated into the sequels. They also became popular with the public after the toys and the Making of special aired on tv. In addition, ILM's special effects staff nicknamed the Millennium Falcon "The Porkburger" but this never caught on.

I like the part at the end where they warn you about spoilers. Watch out! Don't ruin the ending for anyone who hasn't seen it!

See also:

Star Wars goofs
Episode V trivia and goofs
Episode VI trivia and goofs