In European Union jargon, refers to the grouping of African, Caribbean and Pacific countries who are signatories to the Lomé conventions with the EU - basically the former colonies of the EU Member States - which give them some preferential trading conditions, a bone of contention in the EU's relationship with the USA and its client states and the World Trade Organization. The ACP Group maintains a permanent secretariat in Brussels with various bodies in parallel with the equivalent institutions of the EU, as well as an ACP/EU Joint Assembly (linked with the European Parliament).
The ACP countries are:
Some material adapted from http://www.acpsec.org