When data is read or written in one continuous stream. It’s measured in megabytes per second (MB/s).
When data is read or written in many small chunks/files. It’s generally measured in input/output operations per second (IOPS).
The memory cells used to store data in an SSD. NAND degrades each time data is written to it. The terabytes written (TBW) figure indicates the drive’s write endurance—the total amount of data that can be written before it starts to lose capacity.
NAND can store one (SLC), two (MLC) or three (TLC) bits of data in each cell. The lower the number, the faster and longer lasting the drive.