Spa is a place where you go to relax and take care of yourself. It's kind of like going to a playground, but for grown-ups.
When you go to a spa, you might get a massage, which is when somebody rubs your body in a way that makes your muscles feel good. Or you might soak in a big bathtub, called a hot tub or Jacuzzi, which is filled with warm water and sometimes has bubbles in it.
There might also be a sauna or steam room, which are rooms where it's really hot and steamy, and you sit in there to sweat and help your body get rid of bad toxins.
Some spas might also offer special treatments like facials or body wraps, which are like putting special creams or mud on your skin to make it look and feel better.
Overall, going to a spa is a nice way to take care of yourself and feel good. Kind of like going to the doctor, but without any shots!