In bash for, while, and until are three loop constructs. While each loop differs syntactically and functionally their purpose is to iterate over a block of code when a certain expression is evaluated.Until loop is used to execute a block of code until the expression is evaluated to be false. This is exactly the opposite of a while loop. While loop runs the code block while the expression is true and until loop does the opposite.

Source: LXer – How to Use until Loop in Your Shell Scripts