Secondary memory storage of a mobile device
ROM works somewhat like RAM. But instead of it emptying every time you turn off the device, defined as volatile, ROM withholds its data through power loss. Data on a ROM chip is less accessible than RAM.
Flash memory is a technology that is used a lot in SSD storage devices. NAND and NOR chips are forms of flash memory. Usually non-volatile, flash memory is a lot faster than a disc for long-term storage. Though both are solid-state, do not confuse this type of memory with RAM, they are not the same thing.
Internal storage is just your devices built-in storage device.
An internal SD card is a Secure Digital device that the manufacturer builds into the device. The internal SD card is most likely for extra space apart from the internal storage. 
An external SD card is one that the user can install. This is for expansive storage. The user can go buy their own SD card, however big they want, and put it into their device. Some PCs are made with SD card slots. The specific format on mobile devices is micro SD. 


RAM in a mobile device is usually soldered onto the motherboard, vs the modules that can be installed and removed from a PC motherboard.