1. A quasi-stable baryon, forming an isotopic singlet, having zero charge and hypercharge, a spin of ¹/₂, positive parity and mass of 1115.5 megaelectronvolts.Designated Λ. Also known as lambda particle.

2. Any baryon resonance having zero hypercharge and total isotopic spin; designated Λ_JP(m), where m is the mass of the baryon in megaelectronvolts, and J and P are its spin and parity (if known).