There's no difference between co-termination and per-device licenses. It's the same SKU.
Whether it's applied as one or the other depends on the organization that it's applied to.
When converting to per-device licensing the process will generate per-device licenses for every existing license in the organization. After the conversions, licenses are just applied as per-device licenses immediately.
The links provided by @CptnCrnch should help explain more.