The object bounds are the values of a models bounding volume defined on a base record.
In case the object bounds are not set properly in a plugin for the currently installed models (for example a mod replaced the vanilla models with smaller or larger versions), the Creation Kit Object Window has a right click context menu entry 'Recalc Bounds' to update them.
TexGen.exe uses the objects bounds to decide if a record and its model qualify for automatic LOD billboard creation. See TexGen Configuration for more.