Primary key and unique key is same... It is a term of DBMS( Access ).. Primary key is a key which has some uniqueness and helps in non duplicating of data.
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primary key:-

Can be only one in a table
In some DBMS it cannot be NULL - e.g. MySQL adds NOT NULL

Primary Key is a unique key identifier of the record

unique key:-
Can be more than one unique key in one table
Unique key can have null values
It can be a candidate key
Unique key can be null and may not be unique