Roll-off means ?

It means that the amplitude of the transfer function declines at higher or lower frequencies. This is what a low pass or high pass filter does.

This generalized term is used when specific numerical values are not required.

ROLL OFF
is a term for
reduction of amplification
with respect to the lateral bandwidth of a filter reigon
and amplifier bylateral bandwidth
and is assumed normaly to refer to only the upper attenuated{by roll off} protion of an filter or other band pass device
{all amplifiers being bandpass devices}

you have roll on roll off much like a ferry