lonely can be used with definitions like no one around or no sibling so on and so on. But my definition is; a feeling. being lonely isn't necessarily when no one is around it's more where... you feel like no one cares or no one will ever understand. In my experience, it is one of the worst feelings, and if you are feeling lonely just remember people do care! you just have to let someone know.
Even in the crowded streets, she still felt lonely.