Selection (also known as filtering) is used to select specific rows from a table based on a given condition. For example, a selection operation may be used to retrieve all rows from a table of customers where the customer's city is 'London'. The result of a selection operation is a new table that contains only the rows that satisfy the given condition.
Projection (also known as column selection) is used to select specific columns from a table. For example, a projection operation may be used to retrieve only the name and address columns from a table of customers. The result of a projection operation is a new table that contains only the selected columns, and the original table remains unchanged.