Property:Query depth
From Tales of Maj'Eyal
"Query depth" is a predefined property that informs about the depth (numerical value computed on the basis of subquery nesting and resolved property chains) of a query while query execution is being restricted by the $smwgQMaxDepth setting. This property is pre-deployed (also known as special property) and comes with additional administrative privileges but can be used just like any other user-defined property.