What's the meaning of race thoughts?

Racing thoughts are a stream of different thoughts that are difficult to stop or control. Some people actually express these thoughts in rapid succession.

Pretend this is a thought: I have to pick up my clothes at the dry cleaners today, I hate it when it rains, I wonder how Johnny is doing in school, my boss hates me, I wonder what I am getting for my birthday. That is a racing thought that can also be defined as a flight of ideas. Both can be considered a symptom of a mental disorder such as Bipolar disorder or attention deficit disorder.