Flash, Magnetic, Optical
Flash memory is a solid state memory (solid state memory has no moving parts). Because of this, there is less to go wrong and it's access speed is very quick (but not as quick as RAM). Although flash is a type of RAM, it cannot be used instead of RAM because the access speed is not high enough. Flash is also used in the memory on phones and cameras.
This is one of the oldest types of secondary storage, it's so old it's even used in tapes and floppy disks. Magnetic is cheap and holds a lot of data, but it's also very slow to read and write on. Magnetic storage is very vunerable to damage, because is has a lot of moving parts and it can be easily wiped.
It's called optical because to write on and read it, you have to use lasers. The lasers get reflected off small bumps and then a sensor detects where the light is being reflected. Unfortunately is much slower than a magnetic hard disk. Two examples of optical media are CDs and DVDs.