Internal monologue

Internal monologue, also known as inner voice, internal speech, or verbal stream of consciousness is thinking in words. It also refers to the semi-constant internal monologue some people have with themselves at a conscious or semi-conscious level (see Default mode network). Much of what people consciously report "thinking about" may be thought of as an internal monologue, a conversation with oneself. Some of this can be considered as speech rehearsal.

...
Wikipedia