IPTC Tab
IPTC values are metadata, as they are stored in the image files but do not affect the actual image. Basically the metadata summarized as IPTC contains additional information about your image. As this information is saved within the image file it cannot get lost. This eases the workflow a lot as you don't have to care about other files when backing up or sorting your images.
IPTC is usually used to describe the image in detail. There are a lot image database software that use the (IPTC) information saved in images to e.g. fill their descriptive fields. For example you can also use IPTC fields when you try to sell your images. Most online image-selling companies support IPTC tags and read them when you upload your images to their databases, thus you have less work. Adding keywords to your images on your home computer once while developing the photo is much more comfortable and efficient than doing so through the web browser every time you share an image. Multiple "Keywords" and "Suppl. Categories" (Supplemental Categories) can be added/removed using the plus 
and minus 
signs next to them.
There are three buttons:
- "
Reset" resets the IPTC values to those saved in your current processing profile. - "
" copies your current IPTC setting to the clipboard. This is especially useful when you you want to apply the same IPTC values to multiple images. - "
" pastes the formerly copied IPTC settings from the clipboard to your current image.
Technical Details
IPTC strings are handled by libiptcdata. When saving strings, RT sets IPTC_TAG_CHARACTER_SET to UTF-8.