If a conviction or sentence is quashed, it is ruled that it is no longer valid and is set aside.

QC see Queen's Counsel

Quam primum Forthwith or as soon as possible.

Quantum How much, the extent. The amount of money sought in a claim for damages.

Quantum valeat For as much as it is worth.

Quasi As if; as though.

Queen's Counsel A senior and experienced lawyer on whom the Queen conferred this honour. This term was replaced by King's Counsel on the accession of King Charles III. 

Quoad ultra As regards everything else. In pleadings, after the averments for the other party have been admitted or dealt with as not know and not admitted, the rest of those pleadings are dealt with. This is usually done by the statement "Quoad ultra, denied." There then follows an explanation as to why the rest of the other party's pleadings are denied.