These are diplomatic bodies similar to embassies, but while embassies are linked to a single country (therefore they are called 'bilateral', e.g. the British embassy to France), the Perm.Reps (as they are often abbreviated) are accredited to the European Union institutions. Each EU Member State has a Perm.Rep in Brussels, and the diplomats working there are representing a Member State towards the European Commission and other institutions.
See also:
EU Institutions | EPSO | EU Institutions | European Commission
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