Identify the term that designates the core repertoire of compositions dating from the eighteenth century to the modern day that is commonly performed at concerts of classical music.?

The term is canon. A canon is a bit of voices sing or play a similar music beginning at various circumstances. A round is a kind of standard, yet in a round each voice, when it completes, can begin toward the starting again with the goal that the piece can go "all around". Maybe the most understood ordinance is the Pachelbel's Canon composed by Johann Pachelbel.

Cthe lindisfarne gospels