It is a little confusing as they have added a couple of additional "Hold" levels.
The manual discusses this starting on page 54.
In a nutshell:
"Channel" is what we are used to with the former Hold button. The scanner holds on the channel.
"Department" is newer. It holds on a group of channels. The new term for group is "Department". (You can also use the Department hold for holding on a single site if you are scanning a trunked system with multiple sites).
"System" is another new type of hold. This will hold on a given system which is in a Favorites List. Typically, Favorites Lists will contain several systems. (Just to gild the lilly, Systems contain one or more Departments with Departments containing one or more Channels. If it's a trunked system, Systems also contain one or more sites.
I found a number of videos on YouTube on the operation and programming of the 536 scanners. They were very interesting and informative when I first got my scanner and embarked on the big learning adventure.