Fixed-rate mortgage
A fixed-rate mortgage has an interest rate that stays the same for the entire life of the loan, so the principal and interest part of your payment does not change.
New Jersey example
Say you take out a made-up 30-year fixed-rate loan at 6.5% on a Toms River home. The rate stays 6.5% for the whole term, which is 360 monthly payments. Even if market rates jump in later years, your principal and interest payment stays the same.
Official source
This is a plain-English summary. Rules and dollar amounts change, so check the official source or a professional before you file or sign anything.