Poker games take many forms. Especially in a home game you will see a lot of things that are called poker but only resemble poker.
Here is the Merriam-Webster definition of poker as of today.
Note the “bets that the value of his or her hand is greater than that of the hands held by others”. I believe this is key number one. This key removes games that are played with cards, and can be played for money, but each game is worth a fixed amount or paid out on points scored, from the poker category. Games like Cribbage, Bridge, and others fit this category. One could arguably put Open Faced Chines Poker in this category as well.
I also believe there are two more keys to make a gambling card game actually be poker. I feel you need to see your hand in order to evaluate it so you can make an educated bet. I also think you must be playing against other players, not the house.
Adding these two extra keys removes games like Blackjack/21, In Between, Night Baseball, and Indian Poker from the poker discussion and leaves them firmly in the realm of a gambling card game.
The focus of this website revolves around my definition of a poker game.