Bandwidth

In information theory, bandwidth is the range a channel spans, and together with signal-to-noise it fixes the channel's capacity: the most it can carry reliably. Widening it is the expensive way to move more.

We use it as a lens. A model's context window is bandwidth you cannot cheaply grow, so the smarter move is to raise the signal in what you send rather than to keep sending more. Encode the channel better instead of buying a bigger one.