Over a year ago I posted an item titled Sensible Metadata Captions. talking about the use (and mis-use) of the image metadata fields such as Title, Headline, and Caption.
A new resource that might be useful is the Metadata Field Guide from photometadata.org. If you’re dealing with image metadata (and if you’ve got more than a couple of images you should be) this can be a useful reference to work out exactly what each of the fields in Photoshop/Bridge/Lightroom/Aperture/ACDSee/PhotoMechanic/etc should be used for.
It’s not a comprehensive list (at a glance I see that it currently doesn’t have “Product” which is one of the options for the Title/ObjectName field in Microsoft’s Expression Media) but it does have a lot of useful information. Check it out!