Arithmetic (operational) intensity
Beginner
How much calculating a job does for each piece of data it fetches from memory.
Novice
How many operations a task does per byte it moves to or from memory, usually main memory. Multiplying two large matrices reuses each number many times, so its intensity is high; adding two long lists of numbers uses each number once, so it is low.
Expert
Depends on the algorithm, the number format, how the work is split into tiles that fit on chip, and how much on-chip memory there is. A larger scratchpad or better tiling raises intensity and moves a task to the right on the roofline.