What refers to a balancing and gymnastics activity that uses a long thin piece of wood or other material that is raised off the ground?

The activity you're referring to is called "balance beam." It is a gymnastics apparatus that consists of a long, narrow platform elevated off the ground, where athletes perform various skills and routines that demonstrate balance, agility, and precision. Gymnasts train extensively to master techniques on the beam, which is a key component of women's artistic gymnastics competitions.