Definition
One-to-one correspondence
One-to-one correspondence pairs each item in one group with exactly one item in another group.
What it means
Imagine giving every cup one saucer. Make one pair at a time. If every cup and every saucer has one partner—and no item is used twice—the groups are in one-to-one correspondence. Pairing also lets you compare amounts without naming the numbers.
Remember it
One item, one partner, nothing left over.
Example
There are 6 paintbrushes and 6 paint pots. Pair each brush with one pot. All 12 objects are used once, so the two groups have the same quantity and form a one-to-one correspondence.
Watch for
Pairing only some items is not enough. A reused item or an item left without a partner breaks a complete one-to-one correspondence.
Common mix-up
A one-to-one correspondence is a complete pairing of both collections, not just a few correct pairs.
Exact meaning
A one-to-one correspondence between two collections pairs every item in the first collection with exactly one item in the second, and every item in the second with exactly one item in the first.