SSD's are solid state discs. Instead of using magnetic media like tape drives or digital information on a disc that spins, the data is saved on flash memory. The pro's are no moving parts and no need to search a spiinning disc to find data.
They should last longer than conventional drives since there are no moving parts. Also SSD's are more resistant to drops and falls as there are no parts to throw out of alignment.
In addition, SSD's are faster than traditional hard drives, so there is a performance difference.