Limited edition means that multiple "editions" or copies of the same artwork exist. When the edition is limited, this means that the edition run has ended and the number of works produced is known and included in the listing.
Similar to limited edition but here the edition run is ongoing. New works are still being produced, which may be numbered. This includes made-to-order works.
With unknown editions, the edition run may have ended but it is unclear how many works were produced.