B films are inherently low budget but far from every low budget film is a B-film. To me, a B film denotes a genre film that is poorly made and innately campy as a byproduct of it's budget and amateur nature (ala The Room or Toxic Avenger). Thus why I wouldn't view Death Proof or The Substance as B films even if there are elements of homage to them within (especially with Death Proof). To me, the Substance is far more influenced by the aueter work of Cronenberg than it is tradition B films. Her other film Revenge, though, is very much influenced by many of the same low budget B films of the 70's that QT is.
Edit: Google AI says:
A B movie is a low-budget film that was originally shown as part of a double feature with a major studio release. The term "B movie" originated in Hollywood during the Golden Age of Hollywood, which was the 1930s and 1940s.
Characteristics of B movies
- Low budget: B movies were made on a small budget and had low production values.
- Formulaic: B movies often had formulaic scripts and tight shooting schedules.
- Short running time: B movies were usually relatively short.
- Genre-based: B movies were often made in specific genres, such as horror, sci-fi, or action.
- Unconventional: B movies often had unconventional storytelling.