Cat grass is any grass that is grown specifically for cats, usually indoors.
It may be grown in a dish from which the cat chews the grass directly or just added to cat food.
The most common stated benefit is to aid the passing of hairballs.
[1] Although cats may favor eating the grass, it has no pharmaceutical effect.
[1] The most common species for growing this grass are oatgrass (Arrhenatherum elatius), barleygrass (Hordeum vulgare), wheatgrass (Triticum aestivum) or ryegrass (Lolium perenne).