Hard disks and solid state drives (SSDs) are internal storage. MicroSD cards are also internal storage in smartphones, tablets, security cameras and other devices. See internal hard drive and microSD.
Safeguard your data and/or increase your capacity with an on-sale SSD or HDD. Especially if you're in the business of video and photo editing or enjoy playing video games.
If you don't have one, or your PC is a bit older, you can still find a great deal on a SATA SSD. These are slower than NVMe drives but they're still a huge improvement on a traditional hard drive.