What is meant accelerator principle?

This explains   the relationship   between   consumption    and investment.

It states that any   change   in consumption spending leads   to a change   in   investment    spending.    Therefore; investments are accelerated when there is an increase in consumption   in the short run.

The accelerator refers  to the number   of times  the  initial  change  in consumption(ΔC)  multiplies   itself  to give  a final  change  in induced  investment(ΔI).