The notation f: ℝ² → ℝ represents a function f that takes input from two-dimensional real numbers (ℝ²) and outputs a single real number (ℝ). This means that for every ordered pair (x, y) in the two-dimensional space, there is a corresponding real number output from the function. Understanding this notation is essential because it highlights the relationship between the input values in multiple dimensions and their resultant outputs, which is crucial for analyzing domains and ranges in multivariable contexts.