Crown or Profile:

A baseball hat crown or profile refers to the top of the front of the cap above the brim. The crown of the cap is made up of panels. There are typically 6 panels, but they do have 4 or 5 panels as well.
There are generally four types of baseball hat profiles: A) Structured – standard high Pro crown profile, B) Mid crown profile, C) Mid to Low crown profile, and D) Unstructured – low crown profile.

Panels
Panels are different pieces of fabric that make up the top of the cap. There are usually five or six panels in a baseball cap.

Brim (also called bill or visor)
The brim of the cap is the piece that protects your face from the sun. It is usually made of plastic which is sewn inside of fabric.

Eyelets
Refer to the small holes on each panel of cap that allow your head to breathe. They could either be metal or reinforced stitching.

Top Button
The jewel on top of the crown that helps hold all the panels together. It is either metal or Plastic and is covered with the fabric used on the cap.

Buckram
The buckram of a baseball hat is the liner inside of the front of the cap that provides the structure and form. Structured caps have buckram and unstructured caps have no buckram, giving them the more casual, lower profile.

Sweatband
The band of fabric lining the inside bottom of the crown that touches the head. Depending on the fabric, the sweatband can make the cap very comfortable and can also help wick moisture away. The cooling sweatbands reduce the temperature of the fabric by 5 degrees or more.

Sandwich
It is the layer between the top and bottom of the visor that is normally a different color or can have a woven label with a logo on it.

Closure
The feature in the back that determines the fit/size of the cap. There are fitted, stretch fit, and adjustable closures.