Kickboxing means fighting with hands and feet (punching and kicking). In sport versions of this general martial arts concept, gloves are usually worn, and elbows & knees are usually against the rules, however some forms of competitive kickboxing like Muay Thai do allow elbows and knees, and of course the pure martial art that’s not bound by sport has no rules.
The term kickboxing covers a very broad spectrum of martial arts and sports. Some kickboxing classes are very basic and non-competitive – you’ll learn similar things to what you’d learn from a Karate or Taekwondo class, just with a little less cultural or traditional context. Other classes are very competitive and can be quite rough.