Is vanilla extract powder or liquid?

It can be either. It can also be a paste or gel. Liquid formulations are more commonly available. Powdered vanilla extract, though harder to find in stores, is used when trying to avoid increasing the moisture content of the mixture, such as in cake frosting. Powdered vanilla also tends to be whiter and does not discolor white or pale-colored frostings in a way that liquid (brown) vanilla extract does.