You're thinking of
lupulin! Yes, it is essentially hop kief.
"Ever look at a whole cone hop and see a yellow powder clinging to the green leaves? That’s lupulin, a naturally occurring substance in hops that plays a large part in giving the plant its characteristic scents and flavors.
In other words, lupulin contains many of the hop acids and essential oils that make beer so delicious. In fact, when brewers add hops to their beer, it’s largely with the intention of extracting these very acids and oils. The plant matter from the hop cone itself is usually discarded."
You're also correct in terms of adding hops at different stages. The classic West Coast IPA is generally wet-hopped, the newer East Coast DIPA styles are generally dry hopped. Wet hopping adds significantly more bitterness, but also preserves the beer (which was the original point of the IPA style), while dry-hopping adds a ton in the way of terpenes.
Dry hopping involves adding hops during fermentation or conditioning. Wet hopping means adding freshly picked hops during brewing (at any point).
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