The History Of Caturday
Adam Rifkin stashed this in Lolcats!
Caturday has been around since roughly 2006. For some perspective that's older than the public version of Facebook, Twitter and almost as old as YouTube.
The tradition is pretty simple. On Saturdays, people on various websites, (starting with 4chan and gaining mass popularity on site "I Can Has Cheezburger") people would post pictures of cats with funny text know as "lolspeak". Lolspeak is a type of broken English, generally grammatically incorrect, almost a type of "baby talk", that can often included well known internet memes. This adds to the humor as you can sort of imagine the cat speaking in that "child like way" to explain the situation it is displayed in.
Putting cats in funny poses with funny text actually dates back to the 1800's such as the example "Five O'clock Tea" below from photographer Harry Whitter Frees.
At six years and counting, Caturday is one of teh Internets' longest running memes.