If you don't respond to the poke then they can't poke you again, it'll tell them "she hasn't received your last poke yet". As they've managed to do it three times you're clearly clicking okay or something. Poking is a feature from original Facebook, people rarely use it now, it's odd for someone to poke you three times without sending a real message or writing on your wall!
Can someone explain it to me please? I 've been poked by the same person about 3 times in the last fortnight, and I'm not sure what it is for. Do i poke back? Is it like saying "hi!" to someone? Thanks