An estimation method where stories get sized as XS/S/M/L/XL instead of numeric points — rougher, faster, no false precision.
Example: 'That's obviously an M, let's not spend ten minutes debating 5 vs 8 points on it.'
In practice: Good for quick, low-stakes sizing early in grooming. Teams usually convert sizes to points later for sprint planning since burndown/velocity math needs numbers, not letters.