The difference between a regular memory card and an SD card is that the SD card is usually smaller in size and is a micro memory card.
Both SD cards and regular memory cards use memory as storage for the data but the SD card only works in devices that have an SD slot and the SD card usually holds less data.
A memory card is usually larger in size than an SD card and the slot they fit in is usually different as well.
The memory cards can hold much more data than any SD card can.
The SD in the SD card stands for Secure Digital.
Also the SD Cards are limited to 2 GB of storage while other memory cards are not limited as of now and can hold a ton more data than any SD Card can.
SD Card storage is older than regular memory cards too.