SkySista,
No, a sideslip and crabbing are different.
When you're crabbing you are (or should be) flying the aircraft in a perfectly balanced state - i.e. ball in the middle, wings level etc. The 'crabbing' bit comes from the difference between your progress through the air mass you're flying in and the movement of that air mass over the ground. In order to line up with the runway in a crosswind you need to point the aircraft into the wind; the stronger the wind the bigger the angle for any given speed. The aircraft is pointing somewhat into the wind, but its path over the ground is different, and hopefully in line with the runway. It's exactly like swimming across a river to reach a point directly opposite - you have to point yourself upstream in order to go straight across.
Sideslipping is a different thing, but it can also be used to hold a runway heading when you have a crosswind. It involves banking the aircraft into the wind to compensate for the drift, but at the same time using the rudder to keep the nose pointing down the runway. With a wind from the right you’ll end up with the right wing down but left rudder applied. This is so-called unbalanced flight - the ball won't be in the middle and the controls will be 'crossed' i.e. the ailerons and rudder will be applied against each other compared to the way in which you’d normally carry out a turn.
In this context it's known as a 'wing down' approach. The advantage is that it allows you to compensate for crosswind while remaining aligned with the runway. It also means there’s no need to align the aircraft with the runway at the last moment before touchdown – you simply land with the upwind wheel first. Some people (including me) prefer it to a crabbing approach, but it depends somewhat on aircraft type since some are better than other at sideslips, on some sideslips are not allowed with full flap and in others they’re not allowed at all.
The other thing that sideslips are good for is losing height in a hurry without gaining speed. This technique is especially handy in aircraft without flaps, but works well in anything where sideslips are permitted.