A Shout-Out is something subtle (a name, line of dialogue, or prop) in a show that refers to fans or family members of the cast or crew, or to another source of inspiration. By nature, these can be obscure for casual fans. In English class, it is known by the more proper-sounding name, an allusion. However, remember that many tropes, symbols, and such are older than they look and can, often, arise in parallel. So despite (or because of) the ubiquitous nature of some creative properties that doesn't mean that anything that seems somewhat similar is referencing said work.