Primary Key
A primary key is a column (or group of columns) used to identify a row uniquely. They allow us to discern easily what columns to use when joining tables.
Foreign Key
A foreign key is a field (or group of fields) in a table used to uniquely identify rows in another table. It is defined in a table that references the Primary Key of another table.
The table with the foreign key is known as the referencing or child table, whereas the table which the fk refers to is known as the referenced or parent table.
Note
A table can have multiple foreign keys depending on its relationship with other tables.