Discrimination in design comes in two forms. One is through direct action. When you see benches designed to prevent homeless people from sleeping on them, that’s one example. Many more examples can be found in this ProPublica piece: Discrimination by Design — ProPublica.
Ignorance is the second way discrimination can occur in design. Just this week Twitter rolled out an audio feature that is inaccessible for deaf people. No one at twitter set out to discriminate against deaf people. The designers at Twitter just didn’t take them into account. (Apparently Twitter doesn’t have an accessibility review team for their software updates, which is bad for a technology company as large as they are.)
Keep in mind both forms when you see something that seems designed to discriminate against certain people. It may be intentional, or it may be an omission. Either way, steps should be taken to eliminate that discrimination.
(More on twitter’s audio tweets, here.)