I am no expert but in my view it is a piece of card or similar which you place under the card which you are about to cut. The blade will cut through your mat and inevitably project a little further. This being the case you would not want it to score your dining room table or whatever you use as a table. A slip sheet (or a base sheet of card) would take this scoring and as it is soft card would not damage or 'dull' your blade. In other words it can be regarded as a table and blade protecter. This is a U.S. product so the term 'slip sheet' is unknown to me in this context (U.K.) It is therefore only my opinion. Best wishes.
Merci !
What is a slip sheet.
I am no expert but in my view it is a piece of card or similar which you place under the card which you are about to cut. The blade will cut through your mat and inevitably project a little further. This being the case you would not want it to score your dining room table or whatever you use as a table. A slip sheet (or a base sheet of card) would take this scoring and as it is soft card would not damage or 'dull' your blade. In other words it can be regarded as a table and blade protecter. This is a U.S. product so the term 'slip sheet' is unknown to me in this context (U.K.) It is therefore only my opinion. Best wishes.
Yes, Tony is correct--it's a scrap piece of matboard, used exactly as he describes.