What definition (and theorem) is dynamically illustrated below? [br](Feel free to move the white point anywhere you'd like!)
[color=#000000][b]Definition of a Hyperbola:[/b][/color][br]A hyperbola is a locus (set of points) in a plane, the [color=#0000ff][b]difference[/b][/color] of whose distances from [color=#000000][b]two fixed points (called foci)[/b][/color] is [color=#0000ff][b]constant[/b][/color]. [br][br][color=#000000][b]Theorem:[/b][/color][br]The value of this [color=#0000ff][b]constant difference[/b][/color] in a hyperbola is equal to the length of the hyperbola's [color=#0000ff][b]transverse axis[/b][/color].