Similar to the "Lobster" or the "Boo", the "Unreachable" is the person that you've liked/loved in the past, had a strong connection with, and always end up thinking about every now and then; the only difference is that you never really had them to begin with.
Phyllis: You mean your lobster?
Lisa: No, hoe, my unreachable....
"He lost his phone" UnReachable
"His phone is out of battery" UnReachable
"I don't know he wont answer my calls or text's" UnReachable