An ordinal number indicates position or rank — first, second, third, etc. Cardinal numbers count quantity (one, two, three), while ordinal numbers indicate order.

What are the ordinal suffixes in English?

Use "st" for numbers ending in 1 (except 11), "nd" for 2 (except 12), "rd" for 3 (except 13), and "th" for all others.

Why is 11th, 12th, 13th not 11st, 12nd, 13rd?

These are exceptions because they come from Old English. The teens (11–13) always use "th" regardless of their last digit.