Locked
This is a property used only for grouped object. This is a local property, so if there is a group inside another group, the user will first need to unlock the bigger group, then, unlock the group inside and, finally, you will be able to change the properties of the objects inside the smaller group.
When unchecked, it is possible to change the properties of every element inside a group.
When checked, it is only possible to change the properties of the group as a whole.