Unlike an internal drive, which is fitted inside your computer, an external hard drive is a device that you plug into it from the outside, and which provides you with more storage space for your files, images, videos and other data.
The cheapest and simplest type is known as an external desktop drive, and contains a single hard disk.
Even the lowest capacity desktop drives now offer at least 2TB of storage, which is enough for over 500,000 JPEG images; plenty of space for the average user. And with top-end desktop drives packing up to 16TB, you'll struggle to fill them even if you shoot high bit-rate 4K video.