Definition
Ordinal number
An ordinal number names a position in an ordered sequence, such as third or 8th.
Continue from this idea into connected AXIO math.
Boundary check: Direction matters: these places are counted from the stated starting end.
What it means
Ordinal numbers answer “which place?” rather than “how many?”. Words such as first, second, and third, and symbols such as 4th, name positions after an order has been chosen.
Remember it
Cardinal counts the group; ordinal names the place.
Example
Five books sit on a shelf. Counting from the left, the blue book is third. Five tells how many books there are; third tells the blue book’s ordinal position.
Watch for
If you count from the other end, the same object can have a different ordinal position.
Common mix-up
3 tells a quantity; 3rd names a position.
Exact meaning
An ordinal number identifies a position in a specified order. The starting point and direction of the order must be clear.