EMMC

eMMC ("embedded MMC") is compact solid-state storage in the form of small on-board devices that adhere to the MultiMediaCard standard. See: https://en.wikipedia.org/wiki/MultiMediaCard#eMMC

From a practical point of view - and for the sake of simplicity - you may think of eMMC as an "onboard SD card".

This also implies that existing MMC drivers will work for both ('removable') SD cards and ('fixed') eMMC storage, with little to no change.