The term 'get together, informally' can be expressed in two different ways. The first is 'sesh', which is a four-letter word that is commonly used in the UK and Ireland to refer to an informal gathering of friends. The second is 'reune', which is a five-letter word that is derived from the French verb 'reunir', meaning 'to reunite'. Both words refer to a casual gathering of people for socializing or other activities.