also: せいそう
noun
Refers to grass that is green and growing, often in contrast to dry or withered grass. The reading あおくさ is the everyday term; せいそう is a formal or literary variant.
春になると、野原に青草が一面に生える。
In spring, green grass grows all over the field.
牛が青草を食べている。
The cows are eating green grass.
Compound of 青 (あお, 'blue/green') and 草 (くさ, 'grass'). The reading せいそう is the Sino-Japanese on'yomi reading of the same characters.