If you have a local definition, please share it with our community. This is the one from San Francisco State University – as defined in our Online Education policy. (This is the 3rd or 4th revision since 2012, and I think there are still some word changes we should consider.)
“HyFlex courses are class sessions that allow students to choose whether to attend classes face-to-face or online, (e.g., synchronous, asynchronous, bichronous).” (Reference: https://senate.sfsu.edu/policy/s21-264-revision-f20-264-online-education-policy-current)
Brian