NICF accredited fitter exam. help needed

hi, i am currently working my way through exam ive been sent to become an accredited fitter with NICF, all going well, basic stuff apart from 1 questio.

BS 5325 2001 states what under the heading of interlay?
I don't have a copy of the BS and google searches haven't helped, I don't really want to fork out £200 for a copy.
can anyone help me out? not looking to be given the answer, just a point in the right direction would be good.

Thanks

 

There is a copy of BS5325(2001) somewhere on this forum. Helpfully unhelpful enough?

 

i did a search on here but didn't find anything. I shall take another look

 

This might help

 

legend