Fixed means the note rate does not move
A 30-year fixed loan has a note rate that stays the same for the life of the loan. The payment of principal and interest stays the same. Taxes and insurance can still change. That is the product most people should start with, not because it is virtuous, but because the payment is knowable.
An ARM is a schedule, not a surprise
An adjustable-rate mortgage starts with a fixed period (often 5, 7, or 10 years) and then adjusts on a published index plus a margin, inside lifetime and periodic caps. The teaser is not a gift. It is the front of a schedule. If you will sell or refinance before the first adjustment, the lower start rate can be rational. If you will still be in the house, model the worst cap, not the brochure.
What to compare
Start rate, adjustment caps, the index, the margin, whether there is a prepayment penalty, and the break-even against a fixed alternative. We will put those next to each other in dollars. We will not sell an ARM as a personality.
Oregon and Washington files
Both structures exist in wholesale. Availability and pricing move. If a fixed rate is close to the ARM start, the extra complexity is rarely worth it. If the ARM is clearly cheaper and your timeline is short, we will say that too.