What do you mean by relation in the relation model?

In the relational model, all data must be stored in relations (tables), and each relation consists of rows and columns. Each relation must have a header and body. The header is simply the list of columns in the relation. The body is the set of data that actually populates the relation, organized into rows. You can extrapolate that the junction of one column and one row will result in a unique value - this value is called a tuple.The second major characteristic of the relational model is the usage of keys. These are specially designated columns within a relation, used to order data or relate data to other relations. One of the most important keys is the primary key, which is used to uniquely identify each row of data. To make querying for data easier, most relational databases go further and physically order the data by the primary key. Foreign keys relate data in one relation to the primary key of another relation.Besides defining how the data are to be structured as discussed above, the relational model also lays down a set of rules to enforce data integrity, known as integrity constraints. It also defines how the data are to be manipulated (relational calculus). In addition, the model defines a special feature termed normalization to ensure efficient data storage.

This definition was written in the context of Database

Relations in a relation model are how two pieces of data are related to each other.

Tables − In relational data model, relations are saved in the format of Tables. This format stores the relation among entities. A table has rows and columns, where rows represents records and columns represent the attributes.

Tuple − A single row of a table, which contains a single record for that relation is called a tuple.

Relation instance − A finite set of tuples in the relational database system represents relation instance. Relation instances do not have duplicate tuples.

Relation schema − A relation schema describes the relation name (table name), attributes, and their names.

Relation key − Each row has one or more attributes, known as relation key, which can identify the row in the relation (table) uniquely.

Attribute domain − Every attribute has some pre-defined value scope, known as attribute domain.