Parallax scroll has become mainstream, Ian Coyle created the very first parallax website for Nike "Nike Better World" in 2011, nowadays it is overused as a trendy effect but it is a great tool if it serves the user experience, and is perfect for storytelling websites.
The term is derived from the Greek "parallaxis", meaning "alteration". Nearby objects have a larger parallax than more distant objects when observed from different positions, so parallax scrolling can be used to determine distances.
20. Parallax Navigation ☆彡