A patent may be defined as "a grant by the State of exclusive rights for a limited time in respect of a new and useful invention" (Grubb, P.W. 1999, Patents for chemicals, pharmaceuticals and biotechnology, Clarendon Press: Oxford, p.1.).
Patents protect the intellectual property of the inventor, preventing unauthorised people from practicing the invention. Patents are granted for a particular territory, and an inventor wishing to have protection in a number of countries must obtain separate patents in each of them.
The European Patent convention requires in patents that the invention is new, that it must involve an inventive step and that it must be capable of industrial application. These requirements are fairly standard in all countries that have a system of patent application.
More information is available at The British Library : Introduction to intellectual property