Coverages are an Arcinfo-Workstation composite datatype that can contain any combination of points, lines, polygons, and annotation.
Although coverages are an outdated format they posses rigid topology which can be useful from a programming perspective: nodes (line ends) are aware of what line they belong to (ARC-ID), lines know which nodes form the ends (FNODE, TNODE) and also what polygons are on the left and right (LPOLY, RPOLY). In a coverage only single part features are supported, with the exception of holes in polygons, and no features may overlap.
Due to internal limits lines (arcs) may only have 100 vertices.
Coverages may contain points, lines or annotation as basic types with polygons being made from lines (boundary) and points (centroid/attributes) thus a coverage is either Polygon or point-and-line (NET or Link). Coverages support different attribute tables for each of the components: point, line, node, polygon, annotation and tic.
ArcGIS for Desktop still supports coverage creation and building (enforcing topology) with an Advanced level license.