What are open sentences in mathematics?

Open sentences in mathematics are expressions that contain one or more variables and are neither true nor false until the variables are assigned specific values. For example, the equation (x + 3 = 7) is an open sentence because it can be true for some values of (x) (specifically, (x = 4)) and false for others. Open sentences are often used in algebra to model relationships and solve equations. They contrast with closed sentences, which have a definite truth value.