I didn't know that any site, ever, read headline. Interesting.
0x0078 120 Iptc.Application2.Caption String No No 0 2000 A textual description of the object data.
Document Title
Caption (Description)
Keywords
I add Copyright Status and Copyright: my name while I'm at it, because maybe some day the photo will go someplace else. But stock sites strip it out. I also make sure to set the date to the actual date of the photo, not the edit date, because some sites are very picky about metadata matching, file Editorial Caption date, exactly!
Some software identifies it as Caption some as Description. Same field.