Context

Context defines the environment of a user. It contains information about
 * location, indicating where a person is, e.g. indoor
 * people, indicating with whom a person is together, e.g. lecture with students
 * activity, indicating what a person is working with, e.g. updating a wiki page

se wikipedia: http://en.wikipedia.org/wiki/Context_awareness

Context-aware services are services which will take into account the context of the user and adapt the services towards these conditions. Typically rules or suggestions from a Reasoner are used for adaptation of the service.