While this may seem like a rhetorical question, portable chairs have expanded into many different types over the years. So, it may be helpful to see what types are actually available these days.
Folding chairs and travel chairs can be synonyms for portable chairs. However, when most people think of portable chairs, they think of beach chairs, camping chairs, chairs in a bag, or backpack chairs. Generally, these have wooden or aluminum frames, and canvas or nylon seats and backs. They may or may not have arms and can have side-tables, cargo pockets, foot rests, cup holders, and/or canopies. Some rock and some recline. These are great for the beach, park, camping, RVing, boating, fishing, watching sporting events, enjoying outdoor concerts, and tailgating. Lounge chairs for the pool or beach can also portable, and you can find folding director’s chairs and folding bar stools, as well.
Then there is a different type of portable chair, which is not exactly a chair as it has no legs, and that is called a stadium seat. These may have arms with a padded seat and a padded back rest, and are a must if you go to sporting events where you have to sit on the cold or hot, but always hard, metal bleachers.