As of 2019 CE, few universities in the US have a full-fledged disability studies program. Some do offer a selection of introductory courses in the field to undergraduates as a minor; many students enjoy analyzing media representations of the disabled, for example. Often, the professor opens the course with a basic question of definition:
"What is disability?"
Virtually all students (and many dictionaries, including Webster 1913 apparently) have a definition of disability that does not differ in essence from their definition for inability. But the prefix really does matter here. In Latin, "dis" originally meant to take apart, or to take away (see dictionary.com as an easy source on this, though not the best). People who have disabilities do not simply lack abilities to do things; those abilities are actively taken away (some might even say stolen) from them... by society.
Disability studies makes a distinction between disability and impairment. It gets explained on Day 1 like this:
A person who has impaired mobility cannot walk effectively. However, we have wheelchair technology, so this inability can be removed. So a person with a wheelchair is not really disabled... until society starts building stairs.
This concept, that the interaction between a person's capabilities and society's expectations from them produces disability, is the social model that gained traction in the 1970s as a result of the disability rights movement. If this were the dominant model in the US, no student would need to have it explained on Day 1. The dominant model, also known as the medical model for disability, places disability solely in the domain of the individual. According to the medical model, there is something fundamentally wrong or broken about the person's body that needs to be fixed so that they can meet society's expectations. Society does not need to change under this model.
(If this strikes you as unfair, it may be even more difficult for you to inspect the earlier, spiritual model for disability, in which the person's soul needs to be fixed. Some people continue to adhere to this model despite the advance of the medical model, as someone who walks with a white cane may discover when a random stranger approaches them and instructs them to "pray for God to take away your sin, and He will give you sight!")
Progressing through disability studies will result in your professor complicating this model. For example, within the field of disability rights there is a conflict between a population sometimes referred to as "the healthy disabled", whose disabilities are relatively easy to accommodate (especially via architecture), and "the unhealthy disabled", who have chronic illness. How exactly does capitalism accommodate someone with an episodic disability that requires lengthy periods of bed rest or isolation, but who can easily participate in the workplace during periods of remission? If you can't think of a reasonable answer to this question, you're not alone. It leaves even the most vibrant of activists scratching their heads.