It's the smallest possible length at which length can be defined. I brought it up originally because it's a length derived from universal constants; so even if we met aliens who have no understanding of how we measure, or do math, we will be able to translate our distances and their distances using planck-lengths. 1 miles = ______ planck lengths. 1 Blorb = ______ Plancklengths, so you can convert blorbs to miles without ever taking out a tape measure.