It is link by which we contacted to each other. It is a link by which we can understand to other without talking and without telling any things. It is a connection which once connected then we do all work for a particular person which we never thought that we do so for any person and we do it simply.
Its a think that make something must to do in our life for the particular person as I have to talk with, I have to see him/her, I have to make him/her laugh or other many actions and we get a special joy after do so. It is a kind of feeling which gives us both joy and sadness, we get joy when see him/her and get sadness when theres a distance between us.