TL;DR
A multi SIM card is a three-in-one card which can be used in every type of smartphone or tablet.

Extra info
Cutting into your SIM card or pasting parts together - it won’t be necessary anymore! A multi SIM card is composed of three parts (from big to small): standard SIM card, micro SIM card and nano SIM card. You just have to push the smaller card out of it’s bigger holder.

Are you using a SIM card which has became too small for your new phone? You can just switch to a bigger SIM card with the help of a SIM card adapter. You can find such an adapter in almost every electronics store. Just insert your micro or nano SIM card into the adapter and you can go along.