The term "panel chart" is often used interchangeably with:

If the goal is to compare a specific entity against the group, consider "ghosting." For example, in a panel chart of sales reps, keep the specific rep's line bold and colored, while having the "group average" as a faint, grey line in the background of every panel. This provides immediate context.

While panel charts are designed to handle multiple variables, there is a limit. A 5x5 grid (25 panels) is generally the upper limit for readability. Beyond that, the viewer loses the ability to synthesize the information, and filtering or interactivity becomes necessary.