EEA Permanent Residence
This document used to be required if an EEA person wanted wished to permanently remain in the UK.
In light of Brexit, this has now been substituted by the Settled Status. However, Permanent Residence is still required if you wish to apply for a British citizenship as an EEA national.
To be successful, you need to have resided in the UK for a continuous period of 5 years as a qualified person, i.e. an employee, self-employed, student self-sufficient person or a jobseeker.