What does the equation y = 3 represent in R3? What does the pair of equation s y = 3, z = 5 represent?

What does the equation y = 3 represent in R3?
What does z = 5 represent?
What does the pair of equation s y = 3, z = 5 represent?
In other words, describe the set of points (x, y, z) such that y = 3 and z = 5. Illustrate with a sketch.