To call is to match a bet or match a raise. A betting round ends when all active players have bet an equal amount. If no opponents call a player's bet or raise, the player wins the pot. The second and subsequent calls of a particular bet amount are sometimes called overcalls.
The short answer is yes poker still falls under the category of gambling, despite its status as a game of skill. Consider the Merriam-Webster Dictionary definition of gambling: Gambling the practice or activity of betting; the practice of risking money or other stakes in a game or bet.
