Overview of the Introduction to English Land Law - Interest in Land
Interest in land is considered as the other type of proprietary right.
Interest gives the holder such rights to use and enjoy the land physically possessed by another. 

Estate is part of the proprietary right that exist.
Estate gives the holders a slice of time during which they are entitled to enjoy and use the land physically they posses. It gives the holders the right to enjoy, possess and use the land beyond the physical surface area of that land.
​In the case of freehold estate, the holders able to enjoy and possess as well as use the land forever. It is tantamount to actual ownership. 

Overview of the introduction to  English Land law - What is Proprietary Rights ?
Proprietary rights govern the ability of the land owners to use and enjoy the land they  physically possess and also land physically possessed by others. 
Proprietary rights are rights that exist in the land which make them capable of enduring the changes of ownership to the land. 
There are two types of proprietary rights. These are holding an estate in land and interest in land.