Inflation is often referred to as a period of 'superluminal' or 'faster-than-light' expansion (e.g. see article on Wikipedia and hundreds of research papers on the subject). This has always bugged me. What exactly is superluminal about an inflating universe that does not apply to a non-inflating one? I mean in a dust/radiation dominated universe you also get regions which move away faster than light even though expansion is decelerating. If the universe expands at 70 km/s/Mpc then regions farther than 45 Gpc away are moving faster than light with respect to us. So what is it that 'superluminal' is referring to? Is it that de Sitter space has an event horizon (i.e. light will never reach some regions of the universe) in contrast to dust/radiation dominated universe? I haven't really come across any explanation for the use of the term anywhere, despite its ubiquity.