A property is a piece of information like a number or a text string that is attached to a FreeCAD document or an object in a document. Properties can be viewed and - if allowed - modified with the Property editor.
Properties play a very important part in FreeCAD, since it is from the beginning made to work with parametric objects, which are objects defined only by their properties.
Custom scripted objects in FreeCAD can have properties of the following types:
Boolean Float FloatList FloatConstraint Angle Distance Integer IntegerConstraint Percent Enumeration IntegerList String StringList Link LinkList Matrix Vector VectorList Placement PlacementLink Color ColorList Material Path File FileIncluded PartShape FilletContour Circle