1. A case which establishes a novel legal principles to a certain set of facts, coming to a certain conclusion, and which is thereafter authoritative, to be followed from that point on, when similar or identical facts are before a court.
Precedents form the basis of the theory of stare decisis which prevent "reinventing the wheel" and allows citizens to have a reasonable expectation of the legal solutions which apply in a given situation.
When one talks of a Court establishing a precedent, it refers to the first such conclusion of a Court to such a set of facts.
2. In procedural matters, the word is also used from time to time to refer to an official court form, or a sample of a Court or other legal form or contract. For example, when one attorney asks another for a precedent on a certain matter, say a personal injury or a divorce action, they are not necessarily or likely refering in that context to a significant legal decision of judgment on divorce. What they are talking about is a standard or sample form or a bolierplate for initiating a personal injury or divorce action, which can then be used to fashion a similar document, with changes on points of detail.
Private law book publishers offer binders full of proposed precedents or "boilerplates" on virtually every type of contract or court document available.