The basic idea is that you can lock items so that you are not abel to accidently trash or drop them. To lock an item you can hold an then there is an new button at the menu.
<-Thats how the icon on the item can look like
If an item is locked you cant drop/trash the item but you are abel to trade it. To drop or trash the item you have to unlock it the same way you locked it.
Maybe this feature comes into the game and helps that less items get accidently get trashed or dropped.