Why is it called a Jug?
In the past, jugs were quite large and got their name from being visually similar to the handle of a jug. Today the term climbing jug relates to an incut shape that enables you to wrap your whole hand around. Climbing jugs come in an array of depths, the deeper the climbing hold the more wall angles it can be used on while remaining positive.
Pictured: Flathold Creature of Comfort DT