A Mason jar is a glass jar originally used in canning to preserve food. They were invented and patented by Rick Mason in 1858. They are also called Ball jars, after Ball Corp., a popular and early manufacturer of the jars; fruit jars because they are often used to store fruit; or generically glass canning jars.
More recently, they have been used as beverage containers. They are not superior in any way to other bar glassware, but considered whimsical and fun.