Reason:
A true equation is something like x+2x = 3x
It is true for all values of x in the domain. Another word for this is "identity". No matter what we pick for x, that equation is always true.
A false equation would be something like 3x = 3x+1
Subtract 3x from both sides and you'll end up with 0 = 1, which is clearly false.
False equations are known as contradictions. No matter what we pick for x, that equation is always false.
Open equations are equations that have at least one solution, but not every value of the variable will work (like it did with the identity).
In the equation 6-t = 12, the solution is t = -6. No other value of t will work.
Another way to think of open equations is to think of it like an open case.
It's open in the sense that we don't have a definitive yes or no. It depends on what the value of t is.