In the hole poker term refers to the cards that are dealt face-down in stud poker. When the cards are “in the hole” it means that only the person who’s been dealt the cards can see them.
For example, a player might say: “I had a 10, 9 in the hole and an 8 as my door card. The other player raised with a queen in the door. Despite only having a drawing hand, I decided to call his bet.”