The Christ's College Students Union (CCSU) is the body charged with representing all of the students of Christ's College. All Christ's undergraduates and graduates are members of CCSU unless they have chosen to opt out. Rather confusingly the CCSU is often referred to as the JCR (Junior Combination Room), which is the correct name for the society consisting of all undergraduates. Naming the college undergraduate society as the 'JCR' is a tradition that runs at a number of Collegiate Universities, including Durham and the other place.
The JCR has a formal constitution and an elected Executive Committee (the JCR Exec) who organise events through the year, especially Freshers' Week. The JCR Exec look after the undergraduates' common room.
The JCR also run their own web site which you can find at: http://www.thejcr.co.uk