The pronunciation is
Keeron. It is a caption superimposed over usually the
lower part of a video image (as during a news broadcast) or any
predominantly text-based video graphic as used mainly by
television news broadcasts that typically resides in the lower
third.
Although it is often
used generically, it actually comes from the name of the company
whose software allows television producers to add those crawling
words, phrases, and images to their broadcasts.