TPTK is the abbreviation for top pair/top kicker. In poker variants with community cards, it describes a pair made up from one player card and the highest community card where its side card or kicker is the highest kicker possible.
Example (Texas Hold'em):
The player has a pair of kings with one of his cards and the highest community card, hence the top pair. Along with the ace, he's also holding the best possible kicker. There's no possible pair of kings that holds a better kicker and can therefore beat this hand. An opponent would have to have a better ranking hand, two pairs or better to beat the hand.