I've looked around the internet, ... is sometimes a little difficult. ... That's quite a general question! Basically, all types that the database system itself offers, like NUMERIC, VARCHAR etc., or that the programming language of choice offers (int, string etc.) would be considered "atomic" data(base) types. Anything that you - based on your program's or business' requirements - build from that, business objects and so forth, are entities... More on stackoverflow.com

I don’t know in what context the term ‘data table’ is being used here, but generally speaking when we say Entity we are talking the language of conceptual and logical models. When we use the term Table, we are talking about a physical data model (a model with a specific target DBMS or platform). IMHO the term Data Table is a redundant since what is a Table if not a container for Data? More on reddit.com

Again, Class and Entity aren't database terms. I.E. databases and the SQL language don't have the concepts (unless using extensions). There are mapping and modelling systems that use the concepts, and then translate those into programming language metaphors and relational algebra constructs. More on reddit.com

It's not a dumb question at all, most database developers don't know the difference. Let's start with the relational model, since it was formalized first. The RM is a logical data model, meaning it applies first-order predicate logic to the field of data modeling. It decomposes data in terms of n-ary relations (which can be represented as tables), and describes logical dependencies that hold in the data, and defines normal forms of relations that prevent update anomalies caused by redundant dependencies. The entity-relationship model is a conceptual model of data, describing data in terms of entities, relationships and attributes. Although Peter Chen is credited with inventing the model, I believe that the terms "entity" and "relationship" were already in use before his paper was published. There are other models like the entity set model which uses similar terms. Chen was in fact the first person to try to formalize an ER model in terms of the RM, and provided detailed information in his paper on how to map from conceptual ER models to logical relational models. In principle, a data modeler would start by defining an ER model, since it describes data in terms of business entities and the relationships among them. Then, they would map it to a relational model, mapping entities and relationships to relations, attributes to roles, identifying dependencies and normalizing the model. Finally, they would map the logical relations to a physical tables, logical domains to physical data types and foreign key constraints, selecting a primary key from the available candidate keys, and so on. In practice, however, most database developers go directly from conceptual to physical, having never studied formal logic and the RM. Your question contains some basic misconceptions: "a bunch of entities in 2 column tables" and "relationship between each table" mixes different levels of representation. In particular, the notion that relationships exist between tables is a throwback to a pre-relational network data model interpretation of SQL tables, and not a concept from either the RM or the ERM. Now I realize this may sound very technical and confusing. Look up formal definitions of the words that don't make sense and let me know if you have any questions. More on reddit.com