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?
Solitude
Solitude is a state of seclusion or isolation, i.e., lack of contact with people. It may stem from bad relationships, loss of loved ones, deliberate choice, infectious disease, mental disorders, neurological disorders or circumstances of employment or situation (see castaway).
Short-term solitude is often valued as a time when one may work, think or rest without being disturbed. It may be desired for the sake of privacy.
A distinction has been made between solitude and loneliness. In this sense
seen as undesirable, causing loneliness or reclusion resulting from inability to establish relationships. Furthermore, it might even lead to clinical depression. However, for some people, solitude is not depressing. Still others (e.g. monks) regard long-term solitude as a means of spiritual enlightenment. Indeed, marooned people have been left in solitude for years without any report of psychological symptoms afterwards.
Enforced loneliness (solitary confinement) has been a punishment method throughout history. It is often considered a form of torture.
In contrast