Sure Nostraaaa!
A Target and a Focus are two separate things. I'f you've ever seen a hunter shooting at one mob while his pet is fighting another, you'll understand. The hunter has designated one mob as a focus and sent his pet out after him. Meanwhile, the hunter designates another mob as a target, and starts shooting.
It's basically a way of keeping two enemies in your sights. One actively, and one passively. The macro I posted allows a rogue to blind a focus without having to tab or click away from the player that he has targeted.
To use it, you have to assign a key to "Focus Target," in your key bindings interface. Mine is "X." Then you target a player, hit x, and then you're free to switch to another target.
You can also bind a key to Target Focus ("Shift X") Which will put the focus back in your sights for some face smashing.
I like to use pitbull unit frames to arrange how myself, my target, and my focus are arranged onscreen.
Focus macros are ideal for 2v2 arena.