ChainsawAsh said:
"BD-9" and "AVCHD disc" are the same thing. Blu-Ray format on a DVD-9.
No, they are not the same. You could consider AVCHD to be a "stripped-down" version of the Blu-ray Disc format with different specs to BD (bitrate/codec restrictions, etc.)
Technically, BD-9 is inaccurate anyway, since it's burned using a red laser on DVD media, not Blu-Ray media. AVCHD disc is the correct term.
BD9 is an official format for Blu-ray Disc video on a 8.5GB dual-layer DVD. Commercially it didn't catch on as the manufacturing cost of 25/50GB Blu-ray media dropped, but it's popular with home users. (By extension, BD5 is the same on a single-layer DVD, but this is an unofficial format.)