A lawyer or attorney is a person who practices law, as an advocate, attorney at law, barrister, barrister-at-law, bar-at-law, canonist, canon lawyer, civil law notary, counsel, counselor, counsellor, solicitor, legal executive, or public servant preparing, interpreting and applying law, but not as a paralegal or charter executive secretary. Working as a lawyer involves the practical application of abstract legal theories and knowledge to solve specific individualized problems, or to advance the interests of those who hire lawyers to perform legal services. The role of the lawyer varies greatly across different legal jurisdictions.