Deen is a system of life which enacts rules and regulations for all spheres of life. Deen provides guidance for both "personal" and "collective" aspects of life.
Generally, the term Deen is used for following systems:
System of King i.e. ‘Deen ul Malik’ in which a king is considered as sovereign, he constitutes the rules and regulations which are followed.
System of Democracy i.e. ‘Deen-e-Jamhur’ in which authority for legislation is granted to the elected members of people.
System of Allah i.e. ‘Deen-ullah’ in which Allah (SWT) is believed as legislator and His sovereignty is enforced thoroughly. This system is called Islam.
“Today I have perfected your religion for you, completed My favor upon you, and have chosen for you Islam as your system of lifer.” (Maida:3)
When Deen is applied to "Personal Life", then it has 3 aspects (a) Beliefs (b) Ways of Worships (c) Customs whereas, when Deen is applied to "Collective Life", then it has 3 aspects namely (a) Social Systems (b) Economic System (c) Political System
And Allah knows the best.