Release for Fabrication (also referred as Good For Fabrication) - All the engineering documents that are to be used for field construction - normally get to a milestone - Released for Construction. For the class of equipment which are to be manufactured - as pressure vessels, process plant equipment etc - the associated milestone is Released for Fabrication.
Essentially - it gives the details to the manufacturer for him to proceed with fabrication of the said equipment. Release for fabrication is a milestone where the major attributes of the equipment has been approved by the owner for further processing as manufacturing activity. As Release for Construction, Release for Fabrication is also a milestone and doesn't signify the completion of the activity. There are always scenarios where due to design changes, the release for fabrication drawings may change and might be followed with newer revisions of the release for fabrication drawings.