An ordinal is a special word that tells you what order things are in. For example, first, second, third, and so on are ordinals.
When we say "initial ordinal," it means the very first ordinal in a sequence. So, if we have a list of things, like A, B, C, and D, the initial ordinal would be "first" because A comes first in the list.
Another way to think about it is like the starting point when we count. We always start with "one" as the initial ordinal when counting things.
So, to sum it up, the initial ordinal is the first word in a sequence of ordinals that tells you the order of things.