Snapback is an urban slang term for an adjustable flat brim baseball cap. All other design elements are identical to modern, fitted, flat-billed caps as worn by professional baseball players. Snapbacks are less expensive than fitted baseball caps, and have become increasingly trendy in young urban fashion.
Although trucker hats and other types of adjustable baseball caps may be sold with pre-bent brims, usually with a mesh back section, these are not typically called "snapbacks" in urban slang.
Youth culture and hip hop fashion popularised the hat, although it is now popular among many groups.