Snaps are another way that developers package applications to make them installable in Linux. Simlar to Flatpaks they are sandboxed and typically - though they don't have to be - used to run desktop applications on the Linux desktop.
Snaps leverage the SquashFS file system which compresses the software for smaller footprints when installed on devices. When run the packages are uncompressed and mounted - shown in the video when running the 'df -alh' command. Because of the decompression needed when starting the application, sometimes the start up is a tad slower which is also shown in the video.
Snaps have had some controversy because the Snap store is hosted by Canonical and mirrors are not allowed. This organization is done for security, but there are members in the open source community who fundamentally resist this dynamic. Flatpaks would be the major alternative, though similarly, in practice, most flatpaks are hosted in a single instance in Flathub.
More information about Snaps and contributing located below.