A hard drive or solid state drive (SSD) that resides outside the computer's case, typically connecting via USB or eSATA. A USB flash drive is also external storage. See
portable drive and
USB drive.
MicroSD: External and Internal
A microSD flash memory card is external storage when inserted into a microSD card reader connected via USB to a desktop or laptop computer. However, microSD cards are also popular "internal" storage for smartphones, tablets, security cameras and other devices. See
microSD.