We have lots of palm trees in Arizona! The descriptive word you are seeking is called a "boot". The word “boot” refers to the part of the palm frond that wraps around the palm trunk. When someone cuts off the frond itself, this is what is left that is still attached to the trunk and held firmly in place. To remove it is not always an easy task and done improperly (using a chain saw) leads to injuries to the trunk that never heal.