As ProfCrash says, it's the second picking of the season. First flush is the early spring picking and tends towards mild, even delicate, flavours and a lighter liquor. A delightful afternoon tea when you have time to sit and contemplate. Second flush is the second growth spurt, and produces a more full bodied tea with the full characteristic aroma of a Darjeeling and a rich and complex liquor. Later in the season will come harsher and less well-rounded pickings, though some properties do well with an autumn picking.
Most of what you get in the typical tea-bag "Darjeeling" is broken-leafed late season leaves. Strong, dark, and not nearly as complex or interesting as it should be. I personally find second-flush Darjeelings to be a good compromise between price and quality, especially when they come from good estates. First flush Darjeelings tend to be a bit light for my tastes much of the time, though when I'm feeling contemplative on a Saturday afternoon, they're perfectly appropriate.
India Blacks, in general, tend to be quite different from China blacks, though I often think that there's a certain similarity between a good Keemun and a good 2nd flush Darjeeling. They both have a strong nose and a well rounded flavour, though the Keemun is much earthier and less astringent.