To-be is defined as something that which will come in the future.
An example of to-be used as a suffix is in the phrase "doctor to-be" which means a person who will be a doctor in the future.
future; that will be (as specified) in the future: used after a noun, esp. one indicating a family relationship: bride-to-be, father-to-be
That is to be; future. Often used postpositively and in combination: a graduate-to-be.