Raglan shaping generally refers to a particular set of decreases used in order to shape a garment with raglan sleeves, when the garment is knit from the bottom up to the shoulders and neck. (I think it uses increases when knit from the top down.)
Raglan sleeves are usually the easiest for beginning knitters to "tackle", as opposed to set-in sleeves, saddle sleeves, etc.
Usually, mirror decreases are made on the public side of the garment on both the left- and right-hand sides and are made a stitch or two from each end. This also allows for easier seaming of the body and sleeves later.
V = stitch
// or \ = decrease