Coptic language is an Afro-Asiatic language that is a descendant from Demotic.
Coptic language refers to 2 things (like Demotic)
1. It's the final phase/stage of Egyptian language. Some would argue that it's a distinct descendant language. This passed through 3 stages, Old Coptic, Classical Coptic, Late Coptic
2. It also refers to the script to write the language. This also passed through stages the Old Coptic script which varied from no Demotic characters to 12 Demotic characters. The standard script stage, where it's written with Greek letters + 6 Demotic characters (Sahidic) to seven Demotic characters (Bohairic,Akhmimic), or no Demotic characters in Bashmuric