IMHO Perhaps 'the man' would have been impressed by the foregoing very sensible discussion (no mickey take intended) but in an eng exam he probably wants to hear something like..
It's relative motion between the airframe and the transmission due to the flexibility of the transmission mounts. e.g. 212 box hangs on 4 (memory?) endwise-on Lord mounts with a rigid link taking the lift loads to the structure. To control the shuggling around two friction dampers are fitted at the flex mount positions. A rough check for serviceability of these is a 1-2inch cyclic 'stir' in cruise... this will generate a vertical 'lump' which (if dampers OK) will die out after one or two beats.
Recommendation is to approach this check with someone experienced (as a boy I did it with too much enthusiasm, both driver and self not happy with result!)
All the above from 15 year old memory since last touch of a lovely helo, G-BAFN where are you now?, so if it's short on detail I'm sorry!
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Water, please...