Pegboards are boards with holes in them, sometimes to put pegs into, and sometimes to put accessories designed to fit into pegboards (shelves, hooks, etc.)
For wargaming purposes, pegboards can be used as a means to track forces in a campaign game. Place the map over the pegboard, insert pegs as markers to represent armies or area control.
Dollar Tree recently has featured a range of Jot-brand pegboard products. They seem to be going fast, so I am not sure if this is a one-time opportunity or if they will eventually restock. The items are mostly gone already from their online store.
The pegboards come in white or black plastic, roughly 5" x 10" (and 5 holes by 10 holes); there is also a half-size 5 x 5 version. There are tongues and grooves to mate the boards together, although they only provide locating help, they do not attach the boards together. Also note that the pegboards fit together in a certain direction.
To hang the boards from a wall, you need to buy the Adhesive Rinks (one pack for each pegboard). According to the directions, you snap the rinks into the back corners of the pegboard, peel off the paper from the adhesive, and stick the pegboard to the wall. What the directions don't mention is that you'll have to first stick the adhesive on the rinks. (The adhesive squares have paper backing on both sides.) Alternately, the rinks have holes for screwing them into the wall.
I have not seen pegs for sale, so I assume you have to make your own. The holes are ¼" in diameter.
If you've always wanted a pegboard for your wargaming campaigns, consider these inexpensive products as an option. While supplies last, of course.