Solitude is lack of contact with people.
never heard of it before
Oh ok, it's a state of being lonely.  It can be caused by bad relationships, loss of loved ones, deliberate choice, infectious disease amongst others
do people go to counseling for it?
Yes. I believe think  most of us have had short term solitude before it is a period when we decide to rest without being disturbed.
who came up with with this term?
I'm not sure buddy but we often desire it because we want to be left alone or so we can think for ourself
that makes sense