Admin area
TheAdministrator area of your website. In Joomla this would be www.domain.com/administrator, in WordPress it would be www.domain.com/wp-admin/
Frontend
The public facing pages of your site. If your administrator area is www.domain.com/wp-admin/ then the frontend is www.domain.com
Backend
Technically this would be considered as part of your Frontend. Property managers administer their properties in the public facing area of your website, through special functionality that only property managers have. That special functionality (property management features) is the Backend.
PII
Personally Identifiable Information. This is any information stored in the database or logs that can identify a user. This can include IP numbers, Names, Addresses and email addresses.
SRP
Single Room Property, e.g. Villas, Apartments, Cottages. Any property where one booking books the entire property for the booking period.
MRP
Multiroom property, such as hotels, B&Bs, guest houses and campsites. Any property where rooms are booked in the property, but not the entire property itself.