while there are many different types of visas, there are five main categories of iran visas:

1-Iran Touristic Visa
Iran tourist visa is valid for 3 months (it means you can enter Iran within the 3 months of your visa issuing date) and maximum duration of stay is 30 days and is required by foreign nationals who wish to travel to Iran for sightseeing. You can apply to get an Iran tourist visa before departure at Iranian consulates abroad or upon arrival at Iran international airports.
2-Iran Pilgrimage Visa
Pilgrimage visa is issued for foreign Muslim pilgrims for the purpose of visiting the sacred places and shrines of Iran in Iran. It is similar to Iran tourist visa. You can request for Iran pilgrimage visa at Iranian consulates or Iran international airports.
3-Iran Airport Visa (on arrival visa)
we are proud to announce: most nationalities are eligible to apply for a 30 day Iran tourist visa on arrival at the passport and visas offices at major international airports of like IKA(Tehran), Shiraz, Isfahan, Mashhad and Tabriz. Some nations are not eligible for visa upon arrival.
Attention : Sorry,we are not allowed to apply this visa for the citizens of Pakistan, Bangladesh, Afghanistan and Somalia due to the regulations of the ministry of Foreign Affairs
4-Iran Business Visa (single/Multiple entry)
foreign nationals who wish to travel to Iran for economic, commercial, cultural or industrial purposes like trade negotiations, participation in conferences (economic, cultural, etc.), work related issues, or for sports activities required this type of visa
5-Iran visa for Family and friends
Iranian citizens are able to invite their family or friends or any one they want for 30 days, But initially, they must complete the process of inviting and receiving this type of visa