Lonliness

What is loneliness? Is it really being alone? Or is it being alone mentally, when you're around a dozen of people but still you feel a sense of loneliness. What exactly it is?
May be it is different for, different kinds of people.
I,when I'm engrossed in some work however silly it might be I don't feel alone.
For me loneliness happens when in a Whatsapp group no one replies to your message.
When you hang out with your friends whom you know for around 5-6 years but you don't feel that sense of connection. You feel left out.
You crack jokes, you do all the fun stuff just to impress, it doesn't comes naturally as it should and then loneliness kicks in.
You feel miserable for a moment, you come home or sit somewhere and think about everything and anything.
About how many genuine people you have in your life. Does anyone actually cares about you?
When you're gonna find that special someone who is gonna understand all of your thoughts, who is gonna be there for you always.
I sometimes start to dream. Dream about how life would be with that special someone. Thinking all the good stuff that could happen to both of us.
Slowly it fades,something else comes up and you forget about it and loneliness is on pause for sometime. If you don't get distracted, you may cry for sometime which is even better because then you feel a lot more better.
Things get stable and the good phase kicks in. Maybe someone comes to meet you or may be you just start enjoy your own company.