A set of integers that give the orders of the blocks in a Jordan canonical form, with those integers corresponding to submatrices containing the same latent root bracketed together. For example, the Segre characteristic of
is [(21)31(21)] (Frazer et al. 1955, p. 94).
More things to try:
Weisstein, Eric W. "Segre Characteristic." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/SegreCharacteristic.html