Brian Tierney wrote finely about repraesentatio in the medieval councils of the West some twenty years ago. He pointed out that repraesentatio could have three different meanings: The first is symbolic representation or personification, as when a whole community is taken to be figuratively present in the person of its head. The second meaning of our term can be defined as mimesis. Here an assembly is considered to represent a whole society because it faithfully mirrors in its composition all (society's) varied elements. The third meaning of 'representation' is delegation or authorisation.
The last item on this list, jurisprudential concept of "representatio" as agency is, perhaps, one of the most important contributions that the medieval jurists of the Ius commune made to Western legal thought. As Tierney, Post, Queller, Congar, and others have pointed out, the development of the juristic concept of agency during the twelfth and thirteenth centuries had a profound effect on medieval institutions.
Kenneth Pennington, Representation in Medieval Canon Law, 64 JURIST: STUD. CHURCH L. & MINISTRY 361 (2004).