The term extra-high density disk in IT refers to a specific kind of floppy disk with a specific amount of storage capacity. This term is actually a bit controversial in its usage, because of different storage capacity designations for these types of storage media.
In some cases, sellers or others advertise floppy disks with a storage capacity of 2.88 MB as extra-high density or ED disks. In other cases, these types of disks are advertised or sold as enhanced density disks. The acronym, ED, remains the same. For most users and IT purchasers, this is a moot point, since more modern types of storage media have brought exponential increases in storage capacity. Nowadays, it is common to talk about storage capacity for small disks or devices in terms of gigabytes, not megabytes or kilobytes.