Conceptual ER diagrams are the highest level of abstraction and represent the overall structure of the database. They are used to communicate the overall design of the database to users and stakeholders.
Logical ER diagrams are a lower level of abstraction and represent the database in terms of tables, columns, and relationships. They are used to design the database schema and to communicate the schema to database developers.
Physical ER diagrams are the lowest level of abstraction and represent the database in terms of physical storage structures, such as indexes and partitions. They are used to implement the database and to optimize performance.
In addition to these three main types, there are a number of other ER diagram types that can be used for specific purposes. For example, implementation-specific ER diagrams are used to represent the database in terms of a specific database implementation, such as MySQL or Oracle. Reverse engineered ER diagrams are created by analyzing an existing database and generating an ER diagram from the data.
The type of ER diagram that is used will depend on the specific needs of the project. For example, a conceptual ER diagram would be used to communicate the overall design of a new database to users, while a logical ER diagram would be used to design the schema for a new database.
https://www.thoughtspot.com/data-trends/data-modeling/conceptual-vs-logical-vs-physical-data-models
https://www.visual-paradigm.com/support/documents/vpuserguide/12/13/5963_visualparadi.html
https://www.edrawsoft.com/er-diagram-examples.html
https://codeandwork.github.io/courses/cs/sqlErdSimpleQueries.html