What's the Difference Between an Arbor and a Pergola?

Both arbors and pergolas can be beautiful additions to your backyard. However, it can be confusing what the difference between the two is. They both can contain trellises and are a relaxing place to spend your afternoon outdoors.
So, I decided to look up the two on Britannica Online to clear up the confusion. Here are the definitions that I found:
ARBOR: “garden shelter providing privacy and partial protection from the weather. The name is used for a modest garden building of any material; it has been applied to examples as varied as a wrought-iron shelter at Melbourne Hall, Derbyshire, Eng., and houses constructed of pebbles, brick, or masonry. It is more correctly limited to rustic garden houses that are made up... "
PERGOLA: “garden walk or terrace, roofed with an open framework over which plants are trained. Its purpose is to provide a foundation on which climbing plants can be seen to advantage and to give shade. It was known in ancient Egypt and was a common feature of early Renaissance gardens in Italy and subsequently throughout Europe
An arbor is usually a passageway, gateway or a spot with a single bench for protection from the elements or to denote a sense of arrival in the landscape. Kind of like a threshold or doorway in a building.”
So, in short, arbors are more passageways, or smaller arches with just a single bench. It is a place you can enjoy alone or with one special person. Pergolas, on the other hand, tend to be larger spaces. They can provide shelter for a picnic table, and groups of people can gather under a pergola to enjoy the outdoors together.