The United Kingdom and Colonies (CUKCs) passport was the old form of the British Passport. Prior to 01.01.1949, the primary form of British Nationality was that of a British Subject.
The British Subject status was given to those born within the British Crowns Dominions and, broadly speaking, most British Subjects will have become CUKCs or citizens of independent Commonwealth countries in 1949. Those that didn't became British Subjects without Citizenship.
The British Nationality Act 1981 came into force on 1 January 1983, and divided Citizens of the United Kingdom and Colonies (CUKCs) into three categories:
CUKCs with the Right of Abode in the United Kingdom and Islands (i.e. the United Kingdom, the Channel Islands and the Isle of Man) by virtue of a close connection therewith (e.g. by birth or descent from a person born in the United Kingdom and Islands) became British Citizens.
CUKCs with a close connection with one of the United Kingdom's Dependent Territories became British Dependent Territories citizens (BDTCs). It was possible for a person to acquire British citizenship and BDTC at the same time. For example, a person born in Bermuda before 1983 with a parent born in the United Kingdom would have acquired both nationalities.
All other CUKCs became British Overseas Citizens (BOCs).
There are categories of British national other than these three, but these consist of persons who were not CUKCs before 1983.