Waterproof ratings are measured in "Hydrostatic Head". This is how much pressure a fabric can withstand. Imagine a drainpipe full of water pushing on the fabric, the height of that column of water is the number quoted. So 10K HH = 10,000mm of water column.
Packs in Pocket
Jackets marked with "Packs in Pocket" all pack away in a pocket, this isn't necessarily one you put your hands in!
It is an easy way to store your jacket inside your pack/race vest when you are not wearing it.