There are two primary types of RAM "chips": DRAM and SRAM.
DRAM - or Dynamic RAM - is a chip that requires a constant source of power to maintain the data it holds onto. That means when you switch off a computer the contents of the RAM are lost and cannot be recovered by turning the computer back on. DRAM is very cheap to produce and therefore it's the most common type of RAM you'll find in modern computers.
SRAM - Static RAM - chip doesn't have the same electrical charge limitation. Instead it's like a "state machine" and holds the data after power loss. Because of how it's produced and how it functions it's incredibly fast. Much faster than DRAM. This also means it's very expensive to produce in large units (megabytes and not gigabytes), so you only really find it inside of CPUs as a very small, temporary storage medium.
Whenever you're reading the specifications of a computer system, especially a personal computer from a store, the "RAM" is refering to the DRAM inside of the system. If you read the specifications on a CPU, you'll see things like "L1", "L2", "L3" and perhaps, but quite rarely, "L4" cache. This is the SRAM inside of the CPU's enclosure and is used directly by the CPU for executing instructions, among other things.
At the Cloud level (AWS), you don't need to care about the types of RAM as you'll only ever be provisioning (requesting) DRAM. So when you ask for a server to have 16GB of RAM, you're asking for 16GB of DRAM. The CPU's SRAM is very, very abstracted away from you.
There is a third type of RAM that's the most common across the planet.
Dual Data Rate (DDR)#
SDRAM, or Synchronise Dynamic RAM, is the most common by a long shot and is what allows us to speed up RAM's performance by large magitudes over using just plain DRAM.
SDRAM is more commonly know as DDR RAM. The DDR stands "Dual Data Rate" and just means (at a very basic level) that the RAM "sticks" (the form factor or the "packaging") operate in pairs, and offer a faster access speed than none SDRAM.
This is the most common type and form factor of RAM. It looks like this:
When you look online for RAM you'll see "DDR" being mentioned a lot. That's because it's the fastest type of RAM we have today. The current common type of DDR is DDR4. DDR5 is here too (you can see it above), but it's not as common. DDR6 is on the horizon.
These chip types are packaged onto a circuit board which provides an interface to the chips themselves. This interface takes on a few form factors.