123mkvcom appears to be a (123mkv.com or similar) that historically hosted movie/TV show downloads in MKV format. Such sites are often unofficial / piracy-oriented and may be:
It looks like you're referencing a string: "123mkvcom mkv" . 123mkvcom mkv
While the convenience of 123mkv is a draw for many, users should be aware of several critical factors: 123mkvcom appears to be a (123mkv