A giant star of spectral type G, K, or M that shows unusually strong lines of lithium in its spectrum. Nuclear reactions in or near the core of the evolving star produce beryllium, which is transported by convection to higher layers where it captures an electron to become lithium. The term is also sometimes used to refer to a T Tauri star (which is very young and still forming); in these cases the lithium is likely to have been present in the gas from which the star formed, and will soon be destroyed once the star reaches the main sequence.