What specifically does "Leet" or 1337 mean?

Solution 1:

Leet (or "1337"), also known as eleet or leetspeak, is an alternative alphabet for the English language that is used primarily on the Internet. It uses various combinations of ASCII characters to replace Latinate letters. For example, leet spellings of the word leet include 1337 and l33t; eleet may be spelled 31337 or 3l33t. The term leet is derived from the word elite. The leet alphabet is a specialized form of symbolic writing.

Leet originated within bulletin board systems (BBS) in the 1980s, where having "elite" status on a BBS allowed a user access to file folders, games, and special chat rooms.

Taken from the Wikipedia page for LEET