A column contains the same kind of information. For example, a table that has information about employees has a column for last name and only employee last names belong in that column.
A row is one instance of all the columns in a table. For example, each row in the employee table contains the first name and the last name for one employee. The columns in a table represent entities, relationships, or attributes.
An entity is a person, place, or thing about which the table contains information. The employee table contains information about the employee entity. Each table holds only one kind of row. The relational model requires that each row in a table be uniquely identified. To accomplish this, you define a uniqueness constraint to identify each row in the table. For more information about primary keys, see Comparison of Primary Indexes and Primary Keys.