The difference between these terms lies in the degree of hearing loss and how you can get help to improve your hearing.
Someone who is hard of hearing may be able to get by with basic sound amplifiers and higher volumes. They may not need the same level of care from hearing care professionals. They may also find that hearing aids do not provide much help. However, someone with any level of hearing loss is encouraged to visit a hearing clinic for professional guidance and recommendations.
Someone with moderate to profound hearing loss may find that basic sound amplifiers don’t help them at all, and they need hearing aids. It will very likely be required to visit a hearing clinic and speak with a hearing care professional, such as an Audiologist or ENT. They will test your hearing and prescribe the best possible solution. If your hearing loss is temporary, they can help discover the underlying cause to restore your hearing. If it is permanent, they can recommend a hearing aid device best suited for your specific needs and lifestyle.
Someone who is deaf will find hearing aids by themselves do not help at all. They will need a cochlear implant which requires a very specialized procedure, rehab, and ongoing maintenance.
This is why it is important to know the differences. You do not want to waste time or money trying a solution for one kind of hearing impairment that isn’t meant for your specific condition. Talking with your doctor or a hearing care professional will help you get pointed in the right direction.