You can think of a v shaped sound as if someone took an EQ and made the handles make a V shape. The highs/treble (the higher end of the spectrum, from around as high as a (musical) triangle to as low as a violin or so) are made to be louder and more forward. This will make it seem as though there is more detail. The mids are between the treble/highs and bass/lows, and would be something similar to a guitar (electric or otherwise). Mids add more body to the music. Then there is bass/lows. I'm sure you know a bit about this, since it is the most popular of the range, especially with everyday consumers. The bass is the lows, the thumping, the subwoofer, the deep part of the music. Bass adds more heft, and a lot of people like bass because it is punchy and boisterous.
A V curve (or U curve) has stronger treble and bass, and softer mids. These are usually known as "fun" coloring (coloring is how headphones modify the music, the more balanced the headphones, the less the coloring). Headphones with a big U (or V) curve are great for music that uses a lot of highs and lows, like rap, electronic music, and other such types of music. Mids are usually preferred for rock.
