SOCKS (socket secure) is a protocol for proxy. A socket is an endpoint of communication.
Why is SOCKS named after socket? How are they related?
The original FAQ tells us SOCK-et-S was its initial internal development name.
I would guess this was chosen for the simple reason that it is a proxy for socket based protocols. Only TCP up to SOCKSv4 and then with SOCKSv5 UDP as well.