Parachain vs Parathread

A chain developed with Substrate can at different points in its lifetime assume one of three states: an independent chain with a secured bridge, a parachain, or a parathread. (source)

Subsocial has acquired one of Kusama's parachain slots.

There are currently no plans for a Polkadot parachain, as it may not be possible technically to move in the near future, but we are thinking about it down the road.

Should Subsocial fail to secure a parachain slot in the future, that chain will transition to a parathread.