What is an external flash drive commonly known as?

An external flash drive is commonly known as a thumb drive because it is a small, portable storage device that typically resembles the size and shape of a human thumb. This term has become widely recognized due to the convenience and compactness of these devices, making them easy to carry around and use for transferring data.

While other terms such as “removable disk” can also technically apply to flash drives, they are more generic and do not specifically denote the characteristic shape and form factor that sets thumb drives apart from other external storage options. "Hard drive" usually refers to larger, traditional storage devices that might not be portable in the same way, and "optical drive" pertains to devices that read and write data on optical media like CDs or DVDs, rather than flash memory. Thus, “thumb drive” captures the unique and recognizable aspect of external flash drives.