A hat is an accessory that players wear on their head. It is possible to wear three to one hats on every category at the same time, though not more than this.
Before accessories were introduced in 2016, all accessories were considered as hats. Because some accessories need to be attached to different parts of ROBLOXian bodies, this caused problems with animations.
Triple Hat Feature
After a while, wearing hats got boring to some people. This is why they created programs that allowed you to wear multiple hats. This was called a Double Hat Glitch (DHG), Triple Hat Glitch (THG), etc., based on how many you were wearing. The admins saw this and realized they needed to add the Triple Hat Feature, which would allow you to wear up to three hats without needing to use a user-made program. The Triple Hat Feature was implemented on June 8, 2010. In 2016, when hats were changed to accessories, users can wear up to eight accessories.