It's primarily a skill game, although luck plays a huge role. In any single given hand, luck is the predominant factor in who will win or lose. However, poker players don't play a single hand. They play hand after hand after hand & and overall, skill dominates.
The answer to whether poker is gambling or based on expertise is that it's a little of both. In order to win a hand, a player will need some element of chance, but they'll also need to know exactly what to do with the cards and the situation in front of them.