Backquote notation is a way of writing run-time code that fills in a certain template, allowing that code to be notated in a way more helpful and visible to the programmer than if he had to write that code himself.  Your use of "evaluates" is also misleading, since the reader only READs and nothing here is EVALUATEd.  It is entirely as if a backquote form is replaced by the runtime code that would have the specified result, and the ANS permits the backquote-generated replacement code to be anything that has the same effect.  (However, many bq implementations expand into alternately-named equivalent internal functions, such as sys::bq-list, sys::bq-cons) so that the pretty printer can recognise bq expansions and attempt to reconstruct something equivalent to the original notation when one of these source-code forms needs be printed in a development environment.)