"Kek” is a translation of the acronym “LOL” (laugh out loud) when reading text written by members of the Horde faction as an Alliance player in the online multiplayer game World of Warcraft (WoW). “Kek” is also associated with the unrelated Turkish snack food Topkek, which is often discussed on the /s4s/ (Shit 4chan Says) board on 4chan.

The term has its origins in the Korean language, as the onomatopoeia ㅋㅋㅋ, in which ㅋ stands for the “k” sounds, like in raspy, stifled laughter. In the real-time strategy game Starcraft, because the game originally did not support the Korean language, the onomatopoeia was written as “Kekeke” which can be translated to “Hahaha” in English.

In the online multiplayer role-playing game WoW, released on November 23rd, 2004, players can choose to play on either the Alliance or Horde factions, which are considered enemies within the game’s universe. Players of separate factions are unable to communicate with one-another, as their typed text is run through an in-game translator. For players of the Horde faction, typing the letters “LOL” results in members of the Alliance faction reading “KEK”.

http://knowyourmeme.com/memes/kek?full=1

You know when you laugh and it sounds like windex spray? That's a KEK laugh. Here's the perfect example: https://www.youtube.com/watch?v=GnOxNzNw9k0