The main difference in SIMs is the physical size of the actual SIM card.
Standard SIM: this type of card is mostly commonly found in older devices.
Micro SIM: this type of card is found in the 4th generation of iPhones, Galaxy S5, etc.
Nano SIM: this SIM is smaller and thinner than Standard and Micro.
eSIM: this is an 'embedded' SIM card. There is no physical card to insert/remove and must be supported and enabled by the network or carrier.
Altice Mobile provides a Universal SIM so it fits into various types of devices. Don't worry if you break out the card that is too small, you can pop it back into the larger one - it will still work!