Sure. Closed practice is usually in reference to religious practices. Voodoo/Hoodoo are the 2 most commonly referenced closed practices, but a lot of Native Americans have closed practices as well. It basically means unless you are part of that culture, it is not for you and you should not attempt to practice. You miss a lot of the cultural significance and often cause damage to the practice (using white sage for cleansing rituals is a great example). They are often appropriated and misrepresented as evil.

AAE, while not religious in nature, has a lot of cultural reference and significance. It is often misrepresented and appropriated without regards to the cultural origin.