A more thorough explanation:

A proprietary lease is a type of lease agreement that is used in cooperative apartment buildings. It is a legal document that outlines the terms and conditions of the tenant's right to occupy a specific apartment within the building.

For example, if you are a tenant in a cooperative apartment building, you will sign a proprietary lease that gives you the right to live in a specific unit within the building. This lease will outline the terms of your tenancy, including the amount of rent you will pay, the length of your lease, and any other rules or regulations that you must follow while living in the building.

The proprietary lease is different from a traditional lease agreement because it is tied to the ownership of the cooperative building. When you sign a proprietary lease, you become a shareholder in the cooperative association that owns the building. This means that you have a say in how the building is managed and maintained, and you may be required to attend meetings and vote on important decisions that affect the building and its residents.

Overall, a proprietary lease is an important legal document that protects the rights of both the tenant and the cooperative association. It ensures that the tenant has a secure place to live and that the cooperative association can manage the building effectively.