The term 'Invitation Word' is used to describe the five words that are typically found on an invitation. The first word is 'WHERE' which is a five letter word that indicates the location of the event. The second word is 'PLAIT' which is also a five letter word and is used to describe the style of dress for the event. The third word is 'COME' which is a four letter word that is used to indicate that guests are invited to the event. The fourth word is 'WHEN' which is also a four letter word and is used to indicate the date and time of the event. The fifth and final word is 'Sil' which is a three letter word and is used to indicate the type of event, such as a formal dinner or a casual gathering.