Definitions for one-to-one
Random House Webster's College Dictionary
corresponding element by element.
Origin of one-to-one:
used of relations such that each member of one set is associated with one member of a second set
A personal relationship between two people.
Matching each member of one set with a member of another set.
There is a one-to-one relationship between days with large cash shortages and his workdays.
Involving direct communication between two people.