To put it simply, suspenders keep your pants up.
Removable suspenders give you the ability to un-snap or un-button the suspenders and take them off your pants on the days you don’t want to use them.
Non-Removable suspenders are built into the pants and cannot be removed. Typically these will be “bib” style pants, where the suspenders are attached to longer front “bib” panel to ensure the snow stays out.
None means the pants do not come with suspenders.