Standard hard drives use magnetic platters for storage and come in a wide variety of sizes. Connections are usually SATA but some still use the older IDE or SCSI connectors.
A solid state hard drive (SSD) is a hard drive that uses flash memory to store data instead of the magnetic platters that are used in a traditional hard drive. SSDs use the same interface as normal laptop hard drives (SATA) and are interchangeable with standard 2.5 in. (notebook) hard drives.
The main benefits of SSDs are higher speed and reliability. Since there are no moving mechanical parts like in a standard hard drive, they are quieter as well.