I would venture to guess that the sentence before that explains it. 🙂 Lores is probably just a short way to say “low resolution.”
Digital Submissions:
You may send low resolution (defined as 500 px on the shortest side) digital files on a DVD or you may choose to send it by email ([email protected]). Please forward a minimum of 100 lores images and 5 hi res images.
From here: https://www.kimballstock.com/submissions.asp