Around this, a bunch of practical tooling surfaced (e.g., hybrid log approaches to luminance mapping) to extend the thinking from 8-bit gamma-mapped content presenting ~8 stops of dynamic range to where we are now. If we get away from just trying to label everyting "HDR", there are some useful things people should familiarize with:
1. Color primaries: examples - SDR: Rec. 601, Rec. 709, sRGB. HDR: Rec. 2020, DCI-P3. The new color primaries expand the chromatic representation capabilities. This is pretty easy to wrap our heads around: https://en.wikipedia.org/wiki/Rec._2020
2. Transfer functions: examples - SDR: sRGB, BT.1886. HDR: Rec. 2100 Perceptual Quantizer (PQ), HLG. The big thing in this space to care about is that SDR transfer functions had reference peak luminance but were otherwise relative to that peak luminance. By contrast, Rec. 2100 PQ code points are absolute, in that each code value has a defined meaning in measurable luminance, per the PQ EOTF transfer function. This is a big departure from our older SDR universe and from Hybrid Log Gamma approaches.
3. Tone mapping: In SDR, we had the comfort of camera and display technologies roughly lining up in the video space, so living in a gamma/inverse-gamma universe was fine. We just controlled the eccentricity of the curve. Now, with HDR, we have formats that can carry tone-mapping information and transports (e.g., HDMI) that can bidirectionally signal display target capabilities, allowing things like source-based tone mapping. Go digging into HDR10+, Dolby Vision, or HDMI SBTM for a deep rabbit hole. https://en.wikipedia.org/wiki/Tone_mapping
So HDR is everything (and nothing), but it's definitely important. If I had to emphasize one thing that is non-obvious to most new entrants into the space, it's that there are elements of description of color and luminance that are absolute in their meaning, rather than relative. That's a substantial shift. Extra points for figuring out that practical adaptation to display targets is built into formats and protocols.