What is the set of first coordinates in a set of ordered pairs called?

What is the set of second coordinates in a set of ordered pairs called?

Given the ordered pairs (1, -1), (2, -3), (0, 5), (3, 4), what is the domain?

Which of these relations is a function: F = {(1, 2), (2, 3), (3, 4)}, G = {(1, 2), (1, 3)}, H = {(1, 2), (2, 2)}?

The mapping diagram for inputs {3, 4} gives outputs {0, 2, 2}. Is this a function?

Given the equation y = 2x + 1, is it a function?

For the equation y^2 + x^2 = 9, is this a function?

Which of the following represents a function: y = sqrt(x + 1) or y = x^2 + 4?

What does the vertical line test check for?

If a set of ordered pairs contains (2, 3) and (2, 5), is it a function?