This is the Marital and Civil Partnership Status (KS103) from the 2011 Census. The data provides the marital status of people aged 16+.
The question was:
On 27 March 2011, what is your legal marital or same-sex civil partnership status?
Never married and never registered a same-sex civil partnership
Married / In a same sex civil partnership
Separated but still legally married / In a same sex civil partnership
Divorced / Formerly in a same sex civil partnership which is now legally dissolved
Widowed / Surviving partner from a same-sex civil partnership.
The 2011 census in England and Wales took place on 27th March 2011. It provides a snapshot of the population and its characteristics on that day.
Further information about the census estimates, including details about the methodology is available here: http://www.ons.gov.uk/ons/guide-method/census/2011/index.html