I'm studying terminology and my understanding is usability basically refers to how easy something is to use. User experience is a holistic term in the sense that everything is taken into consideration and it's overall if the user enjoyed using the item. Doesn't that mean user experience always includes usability, since user experience basically includes everything?
You're right in that user experience does include usability, usability is a big part of user experience. You have pretty much answered your own question but I will help to clarify.
Usability is typically how easy and intuitive something is to use. This makes up a large part of how good UX is judged. Usability is just one part of user experience, as user experience could also include emotional reactions to using/interacting with something - hence the whole 'experience'.
It is fair to say that user experience would always include usability - as something that is or isn't very usable is very likely to have an impact on the user's entire experience.
Very often good usability will contribute to good UX. Which is unlike good UI (user interface design), which can look great, but not always contribute to an overall good user experience (and can even hurt in some cases).
User experience and usability are both essential for the success of any app or website. However, they are not the same thing.
Usability is all about being able to do something easily, and intuitively, while UX is how a person feels when they are interacting with your website or app. Successful UX means that you know who the users are, know what they struggle with, and know what they are hoping to accomplish.
Usability is definitely a part of user experience, among other things like: information architecture, content strategy, interaction and visual design, journey mapping & user interviews/testing.