A short guide to p-torsion of abelian varieties in characteristic p
  There are many equivalent ways to describe the p-torsion of a principally polarized abelian variety in characteristic p. We briefly explain these methods and then illustrate them for abelian varieties A of arbitrary dimension g in several important cases, including when A has p-rank f and a-number 1 and when A has p-rank f and a-number g-f. We provide complete tables for abelian varieties of dimension up to four. 
Rachel Pries