What does shorted mean?
This means that the aluminum or copper bars are placed in slots with the help of end rings, such that there is permanent contact at both ends. This means they are electrically shorted and leads to a very small resistance in the rotor.



In response to your comments below:

Short circuit and shorted are the same thing. 

In circuit analysis, a short circuit is defined as a connection between two nodes that forces them to be at the same voltage. In the example above shorted means the bars are in contact at both ends.