The solution ORMs provide is to “map” an object class, which is a type (or domain), onto a table, which is a relation variable (a.k.a. relvar). This supposedly abstracts away an “impedance mismatch” between the two. ORMs are already off to a bad start, mapping a type to a variable, but I’ll continue.
The real impedance mismatch is a set of very fundamental differences between application data and data in a well-designed relational database.