Fixed rests are rests that stay in position during the shot. They are usually spring loaded or use a springy launcher blade to provide some cushioning of the arrow. When set up right they offer support for the arrow through the entire shot.
It's not unusual for the the blade style rests to contact the vanes or even the nock as the arrows passes by. With a flexible enough blade this is still very forgiving and won't deflect the arrow.
Blade rests are a favorite of many tournament shooters due to their accuracy and forgiveness.