deviation. 1  the act of deviating. 2  departure from a standard or norm. 3  Statistics. the difference between one of a set of values and some fixed value, usually the mean of the set. 4  Navigation. the error of a magnetic compass, as that of a ship, on a given heading as a result of local magnetism. 5  Optics.
The definition of an invitation is a request for a person's attendance at an event. An example of an invitation is a printed card asking family and friends to come to the sender's wedding. 1  an inviting to come somewhere or do something. 2  the message or note used in inviting.  enticement or allurement.
When receiving an invitation, one is obliged to respond in kind as soon as possible. This means if receiving the invitation by phone, reply by phone, etc. One must accept or decline even if RSVP is not specified. To not do so is an insult to the host.