What does it mean to have sores in mouth?

Something wrong. Having "sores" in the mouth indicates something is abnormal. There are a number of things that could be responsible. You need to have a thorough evaluation and examination by a dentist.
Mouth sores. There are many reasons to have sores in your mouth. Several viruses can cause sores, such as hand foot and mouth, or herpes, but also other sores such as apthous ulcers that occur for a variety of reasons. If you have fever or difficulty swallowing a general physician can examine them and tell you if medication is warranted. Over the counter liquid antacids can help "band aid" the sores.