Sorry, if I can add some information, I have found this description for the Epitaphion:
The word Epitáphios is composite, from the Greek ἐπί, epí, "on" or "upon", and τάφος, táphos, "grave" or "tomb". In Greek the word has, inter alia, the meaning of both the English epitaph and the liturgical one.( It's took from the link provided by teacher Vassiliky).
In addition, the Epitaphion can replace the whole Church, the Holy Liturgy can be celebrated on the Epitaphion alone if there is no place to celebrate It.
Thank you for sharing.