The term 'IS IN SESSION' can be broken down into two words, 'IS' and 'IN SESSION'. The four letter solution for 'IS' is 'SITS', which is a verb meaning to be seated or to rest IN an upright position. The phrase 'IN SESSION' typically refers to a period of time when a group of people, such as a court or legislature, are meeting to discuss and decide on matters. Therefore, the phrase 'IS IN SESSION' implies that a particular group is currently meeting and actively discussing matters.