The term 'RIGHT-ANGLE ANNEX' can be broken down into two parts: 'right-angle' and 'ANNEX'. 'Right-angle' is a term used to describe a 90-degree angle, while 'ANNEX' is a term used to describe an addition or extension to a building. The crossword solution for this term is 'ELL', which is the abbreviation for the unit of measurement 'ELL', which is equal to 45 degrees. Therefore, the term 'RIGHT-ANGLE ANNEX' can be interpreted as an addition or extension to a building that is at a 45-degree angle.