When we don't know if a statement is true or false.
Example: x + 2 = 3
Until we know what the value of "x" is, we don't know if "x + 2 = 3" is true or false.
• If x is 1 then "x + 2 = 3" is TRUE
• If x is 2 then "x + 2 = 3" is FALSE
• etc
See: Sentence