No, not talking about a small bush, but in this case referring to beverages and there are two general types –
We’re talking about mixed drinks, shrub is the name of two different, but related, acidulated beverages. The first type of shrub is a fruit liqueur that was popular in 17th and 18th century England, typically made with rum or brandy mixed with sugar and the juice or rinds of citrus fruit.
The second “shrub” can also refer to a cocktail or soft drink that was popular during America’s colonial era, made by mixing a vinegared syrup with spirits, water, or carbonated water. The term “shrub” can also be applied to the sweetened vinegar-based syrup from which the cocktail is made; the syrup is also known as drinking vinegar. Drinking vinegar is often infused with fruit juice, herbs and spices for use in mixed drinks. A great recipe here.