The high commissioner of the United Kingdom to Belize is the United Kingdom's foremost diplomatic representative in Belize, and head of the UK's diplomatic mission in Belize.
As fellow members of the Commonwealth of Nations, diplomatic relations between the United Kingdom and Belize are at governmental level, rather than between heads of state. Thus, the countries exchange high commissioners rather than ambassadors.
Source: [1]
The heads of British diplomatic missions are persons appointed as senior diplomats to individual nations, or international organizations. They are usually appointed as ambassadors, except in member countries of the Commonwealth of Nations where a high commissioner is appointed. The head of mission to an international organization is usually a permanent representative. For some nations a consul or consul-general is appointed.
A British High Commission is a British diplomatic mission, equivalent to an embassy, found in countries that are members of the Commonwealth of Nations. Their general purpose is to provide diplomatic relationships as well as travel information, passports, dual-citizenship information, and other services between Commonwealth states.