Plans and perspectives
A layer is an organizational concept. A layer is a collection of related objects and results and each object and result resides on one and only one layer. For example, all slab elements are on the Element layer.
Plans, on the other hand, are a display and editing concept. Each plan is a filtered view of all of RAM Concept ’s layers. A plan can be set up to edit a particular layer, but the plan does not "own" the layer. All changes that are made to the layer using the plan will be visible in all other plans, because all plans are viewing the same set of layers.
See Understanding Layers and Using Plans and Perspectives for more information.
This means that more than one object has been selected and they have different values for that property. For example, if you select two slab objects that have different thicknesses then the thickness field displays "conflicting".