Language is very important in creating a welcoming environment for the community. As a general rule, use “person with a disability” or “disabled person” when referring to an individual. Words like “handicapped”, “differently-abled”, “challenged”, or “handi-capable” are frowned upon and shouldn’t be used. Instead of saying “handicapped restroom stall” or “handicapped parking spot”, replace handicapped with the word accessible. This is the accepted terminology.
“Special needs” is contested by many. Parents often use this phrase to describe their children, but many adults in the community do not, and argue that this is patronizing. Autistic vs. person with Autism is also contested, though I would lean toward using “Autistic”, as suggested by the Autistic Self Advocacy Network (A.S.A.N.). My suggestion in general would be to follow the lead of the person you’re speaking with. If they refer to themselves as someone with special needs or as Autistic, use those terms.
Refrain, however, from using language like “crip” or “cripple”, even if you hear someone use the word. This is insider terminology that is only acceptable coming from a person with a disability, in particular a physical disability. Also refrain from using commonly used words like “stupid”, “lame”, “spastic”, and “dumb” and/or “mute”. These words are incredibly hurtful to the disabled community. Preferred language includes identifiers as “little person” or “person with dwarfism”, “intellectual disability”, “d/Deaf”, ect.
I use d/Deaf here to acknowledge the difference between “small d” deaf and “big d” Deaf. The word “deaf” in the lower case refers to both the condition – deafness – and a person. A deaf person is someone with hearing loss who does not associate with the Deaf community, or who sees their hearing loss only as medical. A deaf person may have experienced hearing loss later in life, or have been raised by hearing parents. A Deaf person is one who sees themselves as a part of the Deaf community and identifies with Deaf culture. A Deaf person may have been born deaf to Deaf parents, grown up using A.S.L., and/or attended a University for the Deaf. You can read more about the difference between deaf and Deaf on the Deaf Expressions blog, or a number of other resources found online.
Refrain from saying “wheelchair bound”, but instead say “wheelchair user”, as those who use wheelchairs view it as a freeing device that allows them to be more fully mobile. Words like “invalid” should never be used, nor should “suffers from”, “stricken with”, or “afflicted with”.
When in doubt, follow the individual’s lead, but also remember that it is not their responsibility to educate you on what is appropriate or inappropriate.