SD Cards and USB Thumb drives store data using similar hardware, but they do have major differences.
1
USB drives work with virtually any USB interface and are backward compatible. SD Cards are not backward compatible. Newer SD Cards may not work on older devices and vice versa.
2
SD Cards are used as removable storage in mobile devices. This is a domain that is specific to the SD Cards. So, your cameras, smartphones, tablets etc. will have SD Cards inserted in them for data storage. USB Thumb drives are usually connected to take out or copy in date.
3
It is possible to transfer data from USB thumb drive to SD card and vice versa. This can be very helpful in resolving any incompatibility issues to a great extent.