Speech reading is the proper term for what is more commonly known as "lip reading". Almost everyone supplements what they hear with what they see. Hard of hearing, deaf and Deaf people just speech read more than most.
If you look very closely and train yourself, you can see a lot of the sounds by the shape and movement of the tongue, and lips.
Still, only about 30% of the sounds we make when we talk are accurately recogninzable from speech reading. Many sounds look the same "on the lips", but sound quite different ... for example, the words "bat" and "pat".
Someone relying on lipreading can usually only follow a conversation by adding help from body language, facial expressions, and context. Even then it usually requires some "going with the flow" and even guessing.
Most people with hearing loss don't hear high frequencies well. They will hear vowel sounds the best, since they have a lot more energy than consonant sounds. Frequently, consonant sounds are very low energy high frequency sounds such as "c", "sh", "s", and even the sounds that distinguish "b" from "p" or "d". Some will be easy to see with speechreading, but some will be more difficult. The difference between "cat" and "bat" are quite visible, but the difference between "bat" and "mat" are not quite so easily seen.
Even hearing people don't always hear every word, so everyone relies a little on speech reading, body language and context from time to time.
Becuase people with hearing loss need to rely more on these things, it's important for them to plan where they are going to sit or stand, so that the light is good for them to see well. Good lighting and positioning are some of the things you have control over that can help you with communication.