Newmanoc: actually I think you're right in that "pratt" probably originated with Naim when the two Cos were working closely together. THEN the Linn marketing/sales people did quite a lot of use of that with their dealers. It;s gone out of fashion now I suppose...
Loosely defined, the erstwhile "pratt" meant a "crispy" sound in the all important 100-10kHz region with close focus on 300-~6kHz: the point was to get FR and phase as good as possible in that range (think of the old LP12).
Much of the music listened to & used for auditioning at the time was rythmic (4/4, 8/4 etc) with vocals. Sooo, if you focused on the main part of the frequency spectrum rather than the extensions -- i.e. your 300Hz blended in well with the 5kHz say -- you had this lively, pleasant sound. I.e. "foot-tapping" sound as the good Mr Tiefenbrun used to say.
Focus on the range & its slight prominence also meant that with speakers reasonably (but not painstakingly) set up, the "springy" effect was still there.
Voila in reductionist and simplified form. Linn & Naim can offer a much more precise & sophisticated explanation, of course. Cheers