Not a term usually used in the bike world. They may be referring to roller brakes which do have a servo action.
If it's those, they work on the principle of rollers rolling up ramps and binding within an outside track, relatively maintenance free but not quite as effective as most other types.
Another servo possibility is the band brake, but those are only on rear wheels so that's unlikely.
We have a number of Cyclanmatic owners so no doubt one will confirm if they are roller brakes.
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