SLC (Single level cell) and MLC (Multi level cell) are 2 types of SSD drive technologies. Both SSD technologies are based on NAND-based non-volatile memory.
Multi-Level Cell (MLC) and Single-Level Cell (SLC) are based upon the same technologies, but they are made for 2 different purposes. SLC is for high performance and MLC is for higher storage. MLC has twice the capacity capability of SLC because MLC stores 2 bits of information per cell as compared to SLC which stores one bit of information per cell. Typically MLC offers a larger capacity, usually twice as much as SLC because of how the data is stored.
MLC comes in at a cost appropriate for consumer products including cell phones, digital cameras, USB drives and memory cards.
The life expectancy of the SSD drives is estimated to be longer than the hardware in which it is contained, although they haven't been around that long to test the theory. SLC lifespan is far greater than MLC's lifespan. The average lifespan of an SLC drive is on the other of 10 to 1 as compared to MLC.
SLC offers a lower density, but it does provide enhanced levels of performance in the form of faster write speeds. SLC stores only one bit per cell which decreases the likelihood of errors.
SLC also allows for longer write/erase cycle endurance and has a life expectancy rated at approximately 100,000 cycles, making it a better fit for use in applications requiring higher reliability, increased endurance, in a multi-year product life cycle.
SLC is priced higher than MLC because of it's speed and reliability.