1. Also known as xi particle.

2. Collective name for the xi-minus and xi-zero particles, which form an isotopic-spin multiplet of quasi-stable baryons, designated Ξ, having a hypercharge of -1, a total isotopic spin of ¹/₂, a spin of ¹/₂, positive parity, and an average mass of approximately 1318 megaelectronvolts. Also known as cascade hyperon; cascade particle.

3. A baryon belonging to any isotopic-spin multiplet having a hypercharge of -1 and a total isotopic spin of ¹/₂; designated by Ξ_JP(m), where m is the mass of the baryon in MeV, and J and P are its spin and parity (if known); the Ξ_3/2 + (1530) is sometimes designated Ξ*.