For example, I have seen the term "LiveCD" in this web page: https://help.ubuntu.com/community/LiveCDCustomization
Why is it called a "LiveCD"?
And is ubuntu-20.04.2.0-desktop-amd64.iso also a LiveCD image?
From What is LiveCD? - Computer Hope:
The name of compact discs that contain an operating system and often other programs. LiveCDs are capable of running on the computer without having to be installed and hard drive storage space is not required. These CDs are also a way for users to try an operating system without having to format their hard drive and install it. For example, many Linux distributions are available in LiveCD format allowing Microsoft Windows users to experiment with Linux without having to erase Windows.
Many LiveCDs are saved as an ISO image, allowing a user to create a CD directly from the ISO without having to set up the CD manually. An example of a LiveCD is the Anonym.OS LiveCD, an OpenBSD OS designed to help keep the user anonymous on a network and the Internet.
And no, ubuntu-20.04.2.0-desktop-amd64.iso isn't a LiveCD until you make it a LiveCD.
