Disability: There are many different ways to define disability, but a good starting point is this: a physical, mental, or emotional difference that is viewed as "outside the norm" for a body or mind, and is devalued by society.
Nondisabled: People whose bodies, minds, and emotional processing generally or mostly match society's expectations for them, in terms of what they are able to do; people who do not have a disability.
Neurodivergent: An identity descriptor used by some people whose brains function differently than society expects them to. These differences might include different styles of learning, different modes of focus and attention, sensory sensitivities, or different needs for social interaction. People who are autistic, or have ADHD, dyslexia, or other learning disabilities might identify as neurodivergent. Usually used to emphasize the variety of different ways brains work, and the value of this diversity.
Neurotypical: A term used to describe people whose brains largely function as society expects, especially in terms of learning styles, focus and attention, sensory processing, or socialization.
Ableism: The force in society that discriminates against and oppresses people with disabilities. It has roots in every other form of oppression, including racism, sexism, transphobia, homophobia, classism, and more, because ableism is the system that judges what bodies and minds are supposed to be, do, and look like. For example, ableism judges that walking is superior to rolling. At the same time, it also determines that people should work eight hours a day, regardless of how much energy they are required to spend on other daily activities, such as walking or getting to and from work when many forms of transportation are unavailable or inaccessible.
Crip: A term used by some disability activists, artists, and scholars as a reclamation of the derogatory term "cripple." It is often used to communicate and foster disability pride, and also resistance to ableism and institutions and forces that support it. Also frequently used by people engaged in intentionally intersectional Disability Justice work.
Mad: Reclaimed language used by some people with psychiatric diagnoses. Though "mad" has been used with negative connotations toward people with diagnoses, some people claim it as a term of pride, asserting that their experiences of different emotional and mental states are a valuable expression of diversity.
Use person-first language, identity-first language, or a mix of both. Person-first language is "person with ___" such as "person with a visual impairment" or "people with disabilities." This language is used to assert that individuals are people first, and that their disability does not define their personhood. Identity-first language is "___ person," such as "autistic person" or "disabled people." This language is used to emphasize that for many disabled people, their disability identity cannot be separated from their personhood; their disability is part of who they are, not something that they "have." Many scholars, activists, and disability communities prefer identity-first language, but many also still prefer person-first language. When talking about groups of disabled people in general, both forms are acceptable.
Avoid euphemisms. Examples to avoid include: "differently abled," "people of all abilities," "disAbility," "handicapable," and "people of determination." These terms imply that disability is a bad word, rather than simply a part of how someone moves through the world. "Special" should also not be used to describe people with disabilities, including in expressions such as "special needs" or "special assistance." All people have needs, and calling some "special" and others "normal" further marginalizes disabled people.
When referring to a specific person and their disability, use the language they use for themself, or the language they have asked you to use. If you're not sure, ask. People get to describe themselves however they want, even if their language contradicts these guidelines.