What is loneliness?

I was wondering earlier if everyone means the same thing when they say they're lonely, or does it have slightly different meanings for each individual.

For instance, when I say I'm lonely, I mean I don't feel like anyone loves me. You might counter argue that I have kids and parents that love me, but thoss don't count for this type of love. Neither does the love of friends, etc. 

I truly feel like no one really loves me when I'm lonely. It may or may not be the actual case, but that's what's in my head.

Often when I feel lonely, I feel like I'll always be lonely. And sometimes I'll even say I don't really deserve to be loved. The latter one is only occasionally though. 

Let me know. It's that what you mean when you say you're lonely, or does it have a different connotation to you?