Sketch items:

Vertex: Point located at the extremity of a sketch item or the edge of a shape (solid or surface).

Edge: Base item of a face boundary.

Segment: Base item of a sketch (line, arc, etc).

Curve: Base geometry of the segment. (for example, the curve of a line is an infinite line).

Profile: Set of continuous segments in a sketch.

Section: Set of profiles in a sketch. All the loops of a face forming a section.

Items of shapes:

Loop: Set of base items (edges) of a face boundary. A loop corresponds to a profile.

Silhouette: Exterior contour of a shape seen following a direction.

Surface: A surface is a "skin" empty of material.

Face: Item defined by a face and limited by restrictive curves (edges).

General shape also called Non-manifold shape: Non-supported topology by the modeler, like for example a sketch like a "T" or 2 blocks with a common edge. Generally, an edge is a junction between 2 surfaces, a vertex between 3 edges.