What is an attribute?
It is a particular property, which describes the entity.

What is a Relation Schema and a Relation?
A relation Schema denoted by R(A1, A2, …, An) is made up of the relation name R and the list of attributes Ai that it contains. A relation is defined as a set of tuples. Let r be the relation which contains set tuples (t1, t2, t3, ..., tn). Each tuple is an ordered list of n-values t=(v1,v2, ..., vn).

What is degree of a Relation?
It is the number of attribute of its relation schema.

What is Relationship?
It is an association among two or more entities.

What is Relationship set? The collection (or set) of similar relationships.