The last two posters (Davlo and CPhoenix) explained things very nicely. I'd just like to offer an alternative view on "boost and cut." Another way to do things would be to use an approach that does the "least amount of monkeying" possible, by only cutting the most offensive frequencies. "Boost and cut," as I've known it, usually applies to the process of using a parametric EQ to
sweep through the highs/mids/lows on any given source, find what is the most annoying frequency or frequencies (by "boosting" those to locate them), then cutting them back with a narrow Q, leaving the rest of the sound untouched. If you get into toooo much "EQ carving," you can really %##* things up unintentionally. Better to just get rid of the problematic sounds.
It's the same process a live sound engineer will use to set-up an overall EQ in a new room/environment-- if you've ever seen/heard a soundman "ring out" a system by boosting through each frequency on a graphic EQ, then cutting back the freqs that create feedback... Well it's a very similar approach, except in the studio it's much more "surgical."
There are two ways to use EQ-- Additive and Subtractive. Additive would be giving "more" of something to enhance a sound by boosting certain frequencies (an approach we want to use pretty sparingly). Subtractive is taking away frequencies as a corrective measure; again, we don't want to go crazy, but better to take away crappy sounding freqs than to get into a battle with yourself and your mix by continually adding more of "this," then more of "that" to counteract "this."
So you basically find what sucks, get rid of it, and leave the rest alone, except for very slight enhancements for tone.
Does that make sense?