The metadata model
The entities, fields and relation definitions themselves, as records to explore.
The metadata model
Columns: Entities (with what each one is, Is a (ISA), and how many fields it has), Fields (the entity or relation type each belongs to, its data type and storage, min and max values, whether it is scoped to a domain or an application), RelationDefinitions (type, source and target entity, cardinality on each side, applicability, uniqueness), RelationTypes and DataTypes. Every column shows who owns the definition: the Platform, the Account or the Tenant.
Filter, sort, group and select work as they do for records. The model's own links are relations you can walk: an entity has field its fields, an entity is a its parent, a relation definition has a source and a target entity and is of type a relation type, and a field is typed as a data type. Select an entity and its fields, parents and the relation definitions that use it are highlighted in the other columns. All the model's links are read with the columns, so the paths cover the whole model; the bar at the bottom says how many links there are.
Keep in mind The metadata world is read here and edited in the Metadata Designer. There is no Add record, Edit, Delete or Add relation in it: the column menu, the record view and the column footer say so and link to the designer instead. At tenant scope, a field of a domain the tenant has closed is not shown, as it is not shown with the records.