Question

what is meant by an accelaration of -2m/s

Answer 1

means that velocity is changing by 2 m/s² . 
because acceleration is change in velocity.
 
i hope it helps......

Answer 2

Hello !
Acceleration of -2 m/s² means retardation or the decreasing acceleration
It means if a body is moving at a particular velocity ,its speed or the velocity will decrease be 2 m/sec in each second as it is moving.
I hope u have got it !
Thankyou