You don't say how old the baby is but all babies are born with a soft spot in the skull. It helps when you give birth. Sometimes babies end up with an indent in the soft spot and it's normal but any concerns should be addressed when you go for check ups. As the baby grows the skull will harden and eventually the bones grow together to form a solid skull. When archeologists find skulls they use the different stages of a skulls growth to tell how old someone is! Just an extra fun fact!
It means that the skull bones in the baby's head have overlapped though this is expected to smooth out with time. Even though it is normal in the first few months, it may also be a sign of a serious problem like head trauma. You should contact a pediatrician to be certain.