Someone at the B2 level in English:
Can understand the main ideas of complex text on both concrete and abstract topics, including technical discussions in his/her field of specialization.
Can interact with a degree of fluency and spontaneity that makes regular interaction with native speakers quite possible without strain for either party.
Can produce clear, detailed text on a wide range of subjects and explain a viewpoint on a topical issue giving the advantages and disadvantages of various options.