Loneliness is the state of being alone and feeling sad about it. Your loneliness might lead you to sit at home listening to depressing songs, or it could inspire you to go out and meet people.
You can be alone — and enjoy every minute of it. But from time to time, most of us experience loneliness. It's a feeling of sadness or even anxiety that occurs when you want company. On the other hand, it is possible to feel loneliness in a crowd, especially if you aren't interacting with others, like in a crowded subway car or busy grocery store. Even a place can have a sense of loneliness, like an empty room just after all your guests have left.