Level of Detail is how much detail is included, or to be included,  in the model element, an “input”

Level of Development is the degree to which the element’s geometry can be relied upon by users…. an “output”.

First its important to note that there are varying Level of Development definitions.

For example,the  AIA’s Digital Practice Documents include revised LOD definitions.  The AIA appears to allow the BIMForum to utilize the AIA’s LOD definitions.  Thus the BIMForum LOD Specification is  identical to those published in the AIA’s updated Digital Practice Documents, except that there is a LOD 350 and there is no LOD 500.

Here are the AIA LOD definitions:

LOD 100 The Model Element may be graphically represented in the Model with a symbol or other
generic representation, but does not satisfy the requirements for LOD 200. Information
related to the Model Element (i.e. cost per square foot, tonnage of HVAC, etc.) can be
derived from other Model Elements.
LOD 200 The Model Element is graphically represented within the Model as a generic system, object,
or assembly with approximate quantities, size, shape, location, and orientation. Non-graphic
information may also be attached to the Model Element.
LOD 300 The Model Element is graphically represented within the Model as a specific system, object
or assembly in terms of quantity, size, shape, location, and orientation. Non-graphic
information may also be attached to the Model Element.
LOD 350 The Model Element is graphically represented within the Model as a specific system, object,
or assembly in terms of quantity, size, shape, orientation, and interfaces with other building
systems. Non-graphic information may also be attached to the Model Element.
LOD 400 The Model Element is graphically represented within the Model as a specific system, object
or assembly in terms of size, shape, location, quantity, and orientation with detailing,
fabrication, assembly, and installation information. Non-graphic information may also be
attached to the Model Element.
LOD 500 The Model Element is a field verified representation in terms of size, shape, location,
quantity, and orientation. Non-graphic information may also be attached to the Model
Elements.

(AIA BIM protocol document, G202–2013, Building Information Modeling Protocol Form)