write equation in latex with parenthesis horizontal

Question

How could I write the following equation including parenthesis and description for both terms in latex (predicted well, simple model) ,

Answer 1

With underbrace{}:

$ ... = ... \left\{\underbrace{|| \mathbf{Y} - ... ||^2}_{\text{using underbrace}} + ... \right\}$

Note that the text is in math mode, so for the description you need to use \text{} to switch back to normal text.