Yep 2l and 3l as said above refers to the number of layers. However 3l usally means that there is a layer to protect the water proof membrane on the inside. The membrane is made of tiny holes which stop water getting in but still allow vapor to get out, making the coat breath. If this layer is right next to your skin, the membrane can get clogged by the oils and dirt in your skin. The extra layer helps prevent this from happening, meaning the jacket should stay breathable and water proof for longer.
The one thing to consider with hoddies is not just the water proof rating but also the breathability. If it does not breathe well and you sweet, the sweet will get trapped inside and this could actually make you colder. This is why its inportant to wear good base layers, not cotton.
Overal it coes doen to wear you ski, if it is just cold but dry, then you maybe could get away with a couple of icebreakers and that hoody. If its wet where you ski, you will want somthing more.