Entity Set: Is a set of same type entities. For example All employees having an SSN number.
Attribute: An entity is represented by set of attributes. Example name, SSN, age are the attribute for “Employee” entity. Ellipses representing attributes.
Relationship/ Relationship Set: Association between two or more entities and relationship set is a collection of relationship of the same type. Relationship lines indicate that each instance of an entity may have a relationship with instances of the connected entity, and vice versa. Diamonds representing relationship sets.
A relationship set may involve more than two entity sets as shown in figure below. The entity sets customers, loans and branches may be linked by a relationship “Borrow” which indicates that a customer may avail loan from a particular branch of bank.