Copyright is recognised as a concept the world over, as one of the principal intellectual property rights which the law will protect.
Fundamentally, copyright aims to protect creators of original content from others copying or reproducing that content, or using the content in an unauthorised way, without the approval of the party who owns the rights.
Copyright protects a wide range of original works, including literary, dramatic, musical and artistic works, sound recordings, film and typographical arrangements of published editions.
Copyright protections lasts, in the UK (and in the US), for the life of the author plus 70 years, so a pretty long time. Once that expires, though, the work is in the public domain; it is unprotected and is free for use by the world. This means that if someone is using an original work as the basis for their own project, that person will need to consider whether the original is still protected by copyright.
Copyright affords creators enforceable legal protection with regard to their content. The protection is enforceable in the sense that if protected material is used in an improper or unauthorised way, the courts of law will provide remedies to the innocent party.
The main source of UK copyright law the Copyright, Designs and Patents Act 1988, or CDPA, but the UK is also a party to various international copyright conventions – probably most significantly the Berne Convention – and in addition was, until relatively recently, subject to the jurisprudence of the European Union, from which many of the principles or rules of copyright law have derived.
Copyright does NOT protect anything in the so-called public domain, either because the source cannot be copyrighted, or alternatively because the rights have lapsed.
Facts cannot be copyrighted, and neither can ideas. A simple illustration of the distinction would be a film screenplay which is based on historical facts. On that basis alone, the screenplay will be original and will not infringe any protected right. If that screenplay is based on a particular newspaper story, say, or a specific treatment of those historical facts, then the story itself may be protected.