As in Specialized suspension. Also ASR (Yeti)?

Future shock rear
active suspension ride / race or summink I think

I thought it was originally for : full suspension rig

Fully suspended rear

Floaty soggy rear

I spent some time, years ago, talking to Horst Leitner of AMP Research just after he’d done his licence deal with Specialized – I was one of his customers buying Amp rear suspension ‘kits’ to build my frames, and he was polite enough to give me the news first hand because it was going to directly affect my business.

FSR was ‘future shock rear’ in his understanding’ which made sense as specialized was already selling rockshox co-designed ‘future shock’ forks by that time ( i had a pair on my KHS Montana team titanium )