Pad-limited vs. core-limited
Beginner
Whether a chip’s size is set by how many connection points must fit around its edge, or by how much fits inside.
Novice
A pad-limited chip is bigger than its logic needs because its edge must be long enough to fit all its pads. A core-limited chip’s size is set by the logic inside, and the pads have room to spare.
Expert
(the pitch is the center-to-center spacing). Ways out include staggered or multi-row pads, fewer power pads, or flip-chip bumps, which take I/O off the perimeter.