LCP is DRM standard (.lcpl files), a JSON/XML extension and ISO standard. https://readium.org/lcp-specs/
Came across it in Norwegian e-book store. This page suggests it is in use elsewhere too. Seems to be a format used for lending books too.
Elsewhere I find that Readium 1.0 can be de-drmd easily but 2.5 is more secure from that.