A detailed help on SCOP2 categories can be found here.

The relationships in SCOP2 fall into four major categories: Protein relationships, Structural Classes, Protein types and Evolutionary events. Additional annotation of the SCOP2 entries is provided using a controlled vocabulary (keywords and tags).

The Protein relationships, consists of three subcategories: Structural, Evolutionary and ‘Other’ relationships.  Structural relationships group proteins according to their structural features. Evolutionary relationship category classifies proteins according to their ancestry. The 'Other' relationships category aims to define and annotate relationships such as internal structural repeats, common motifs and subfolds.

Structural classes, organizes protein folds according to their secondary structural content.

Protein types category groups proteins according to their type as soluble, membrane, fibrous and intrinsically disordered; each type to a large extent correlates with characteristic sequence and structural features.

Evolutionary events category provides annotation of various structural rearrangements and peculiarities that have been observed amongst related proteins and which have given rise to substantial structural differences.