You have to chat online to appreciate this one. Basically, it's referring to when you're in a conversation online with someone and they respond to something you just wrote by writing "k," meaning "okay." But by itself, no other words, and only with one letter - it kind of suggests a blow off, like they're not interested in continuing the conversation, and they're kind of rude (totally depends on context, sometimes "k" is fine).
Include your pet's photo in our rotating archive by sending it to firstname.lastname@example.org. Make sure you put "pet" in the subject line, and tell us something about your pet (goofy, touching, whatever you like), and we just might write a post about it too!