The hash identifier of the activity that's been chosen to be considered the canonical "conceptual" activity definition. This may have many variants, defined herein.
Mapped to DestinyActivityDefinition in the manifest.
The hash identifier of the most specific Activity Mode under which this activity is played. This is useful for situations where the activity in question is - for instance - a PVP map, but it's not clear what mode the PVP map is being played under. If it's a playlist, this will be less specific: but hopefully useful in some way.
Mapped to DestinyActivityModeDefinition in the manifest.
The enumeration equivalent of the most specific Activity Mode under which this activity is played.
The activity may have 0-to-many modifiers: if it does, this will contain the hashes to the DestinyActivityModifierDefinition that defines the modifier being applied.
Mapped to DestinyActivityModifierDefinition in the manifest.
Every relevant variation of this conceptual activity, including the conceptual activity itself, have variants defined here.
A milestone may have one or more conceptual Activities associated with it, and each of those conceptual activities could have a variety of variants, modes, tiers, what-have-you. Our attempts to determine what qualifies as a conceptual activity are, unfortunately, janky. So if you see missing modes or modes that don't seem appropriate to you, let us know and I'll buy you a beer if we ever meet up in person.