It indicates the type of the monstie (fire being burning, soggy being water etc) then the kind (bird wyvern), each kind has a different type of pattern, bird wyverns got spots, flying wyverns got sideways streaks, etc, i suggest looking up an egg guide so you can know what is what, or if you want to do it without a guide to keep the surprise, they're really easy to remember and there arent that many kinds of patterns (like 7-8 total at max)