The board, skunks, and double skunks
A cribbage board is a track of 121 holes. Every point you score moves your peg forward, and the first peg into the last hole wins. A skunk is winning before your rival reaches hole 91. A double skunk is winning before they reach hole 61.
Why two pegs each
Each player has two pegs and leapfrogs them. When you score, you move the back peg ahead of the front one by the number of points. The peg left behind shows where you were, so a miscounted move can be checked. Boards with three streets of 40 holes snake back and forth, and hole 121 sits at the end of the last street.
Points are pegged the moment they happen, in the play and in the show. That includes counting out mid-hand. If your show gets you to 121, the game ends there, even if the dealer was holding a monster crib. That is why counting first matters.
Skunks and double skunks
If the loser never reached hole 91, they were skunked. League play often counts that as two games. If the loser never even reached hole 61, that is a double skunk, the rarest rout in cribbage, usually scored as three games. Some boards have a small line carved at 91 and at 61 so nobody has to count.
Hole 120 has a name too. The stinkhole is one short of winning, and every count seems to come up empty from there. Some house rules forbid pegging out of it on a Go or a 31.
Muggins, the optional rule
Muggins is a traditional table rule, off by default at most tables. Each player counts their own show aloud, and any points they miss can be claimed by the rival. It punishes sloppy arithmetic and rewards knowing the counting page cold. Agree on muggins before the first deal, never after.