The vanilla flavour of ice cream, cakes, custards and coffee drinks, from cured vanilla pods or, far more often, synthetic vanillin. It flavours sweet foods and drinks, not savoury cooking.
香草 has two main meanings: 'vanilla' (as a flavor, especially in 香草冰淇淋) and 'herbs/fragrant plants' in general. Context usually makes the meaning clear.
history
In classical Chinese poetry, 香草 (fragrant plants) was a metaphor for virtuous people, famously used by the poet Qu Yuan in his work Lisao (离骚).