Contract law

In the civil law tradition, contract law is a branch of the law of obligations. Contract law is based on the principle expressed in the Latin phrase "pacta sunt servanda", (agreements must be kept). The common law of contract originated with the now-defuct writ of assumpsit, which was originally a tort action based on reliance. Contract law falls within the general law of obligations, along with tort, unjust enrichment, and restitution.
It was held in Simpkins v Pays that the parties must also exchange "consideration" to create a "mutuality of obligation," 
A contractual term is "any provision forming part of a contract". Each term gives rise to a contractual obligation, breach of which can give rise to litigation. Not all terms are stated expressly, and some terms carry less legal weight as they are peripheral to the objectives of the contract.
Another dimension of the theoretical debate in contract is its place within, and relationship to a wider law of obligations. Obligations have traditionally been divided into contracts, which are voluntarily undertaken and owed to a specific person or persons, and obligations in tort which are based on the wrongful infliction of harm to certain protected interests, primarily imposed by the law, and typically owed to a wider class of persons.
The law of contract in Bulgaria is known as "law of obligations. "

References - 
https://heinonline.org/HOL/LandingPage?handle=hein.journals/sdintl7&div=24&id=&page=
https://www.austlii.edu.au/au/cases/cth/HCA/1951/79.pdf