Is unregulated gambling actually illegal?

Last night, six friends and I gathered for a friendly game of poker. We each put in $5, and the winner took home $35.

Since none of us has a gambling license, is this behavior illegal? If so, why?

Furthermore, what would have happened in this hypothetical situation: Say, when we got pizza delivery, the Domino’s guy overheard us playing poker and discussing the money in the pot. He, a staunch anti-gambling advocate, was so outraged by this that he called the police. When the police knocked on the door, we let them in, and they observed the poker game and the cash on the table.

What would happen? And what could happen? I’d hope that no reasonable police officer would waste his/her time busting up a friendly game of poker, but technically, could we have gotten in trouble for this? Could we have all been arrested for betting $5 in an unregulated gambling setting? If so, what are the possible consequences?

I feel like any judge would laugh when seven upstanding members of society entered the courtroom, having been charged with betting $5 on a game of poker…

But I’m just interested to know the actual laws surrounding this type of behavior, and I’ve had difficulty finding the specifics online.