Load? *What is this for., The heading under Id Unknown button or Show all Options

[Bear]

Using Activity Master;

One of the headings under "Rolling Stock Available" "Id Unknown button" list or "Show all" list, is "Load?"

Some of these are checked with an "X" and some are not.
What if anything is this category for?

PS:I tried the search feature and got a lot more than I bargained for.
(none of which related to my question.)