A high representative is normally someone appointed to represent an organisation abroad. The former Spanish Foreign Minister and former Secretary General of NATO, Javier Solana, is the Secretary General for the Council and at the same time High Representative for the Common Foreign and Security Policy.
As High Representative he has to assist the Council in Common Foreign and Security Policy. Solana often travels with the President in office or his foreign minister to negotiate on issues such as peace in the Middle East and elsewhere.
The future
The EU Constitution proposes that the High Representative post should be abolished. Instead the EU would have a common foreign minister. This post should be appointed by the prime ministers in the European Council by qualified majority, accepted by the President of the Commission and be subject to approval together with the rest of the Commission by the European Parliament.
The Foreign Minister will function as a vice chair of the EU Commission and a chair of the Foreign Affairs Council (double hatted function).
Links
http://ue.eu.int/en/summ.htm