What is the term for the board running around the bottom of a wall in a room?

The term for the board running around the bottom of a wall in a room is "baseboard." Baseboards serve both functional and aesthetic purposes. They cover the joint between the wall and the floor, protecting the wall from kicks, scuffs, and cleaning equipment while also providing a finished look to the room. They can be made from various materials, including wood, MDF, or vinyl, and come in different styles to suit interior design choices.

It's important to note that while "skirting board" is a term that is often used interchangeably with "baseboard" in some regions, the choice of terminology can vary depending on the local dialect or building standards. However, in the context of this question, "baseboard" is the most commonly accepted term in American English for the board at the lower edge of a wall. Other options like "chair rail" and "crown molding" refer to trim placed at different heights and for different purposes in room design.