The Extended repayment plan allows borrowers to make payments over a longer time period than the 10-year Standard plan (usually 25 years), and therefore have lower monthly payments. Borrowers on this plan may end up paying more over the life of their loan because of interest.
In an Extended plan, the payments can be either fixed over the course of the timeline, or start lower and increased every two years - this would be called Extended Graduated.
To qualify for the Extended plan, there are requirements around the date you took out your loans - you can read more at Federal Student Aid. You also need to have more than $30,000 in outstanding loans.
Payments on the Extended plan don’t qualify for Public Service Loan Forgiveness.