I'm pretty certain he is referring to this:
http://www.youtube.com/watch?v=0eCQ9F1OPvs
 
Similarly heard here (0:08 and 4:08 marks):
http://www.youtube.com/watch?v=65P9y0xSxO4
 
Is regularly found in modern metal, though seemingly a "trade secret" on how exactly to produce. I've come across one or two little VSTs to do a fair job (Subatomic comes to mind), but it may be the case that creating the bass-heavy sine wave from scratch would offer the best result when done right (though I can't say I've yet done so myself).

Check out online for linkin park production. Their music is a bit meh but they have awesome timing and transitions and blend metal and electronica really well.

This is a better example:
 
http://www.youtube.com/watch?v=jmmfyw-8EcI
 
I have just had some experience with this as I am producing a track right now which could be described as aggressive hip hop and the singer wanted some bass drops in the bass line so I had to figure out what she meant and do the research.
 
It is more an aggressive bass sound and it can be programmed from synths like NI Massive. (And many others I am sure) There is often some fairly severe effects that are applied after the synth too. But there is a simpler way as well. If you have got Camel Audio's Alchemy or the Alchemy player they have a great library called Dubstep and all those bass sounds are in there. The MixPads allow for some pretty wild operator manipulation too. They rock!

pauxier, fyi, dropzone would probably not be a good choice. Romplers typically are bad choices for such things and are better suited for emulating real instrument sounds. Massive is by far the most popular choice for this sort of thing, but if you want t stick to Cakewalk plugins, it is more than doable.  here are a couple of expansion packs for z3ta+ that will have presets that may work for you:
 
http://www.store.cakewalk.com/b2cus/ProductInfo.aspx?productid=30-XSDD1.00-20E
 
http://www.store.cakewalk.com/b2cus/ProductInfo.aspx?productid=10-CWZ32.00-2CE
 
 

The Xenos Soundworks z3ta presets appear to be on permanent sale here

So, bass drop refers to the type of sound and not a particular articulation or motif/pattern?
 
The sine wave trick is used a lot to give a bass more depth--if that's what we are talking about.  Doesn't work for my style but I have heard it a lot and it can be cool.
 

Konrad,  keeping up with the various terms thrown around in various sub-genres can be a challenge and you will encounter variations in meaning of the exact same term.  Most of the time , the "drop" refers to a moment in the song where some variation of section extremely heavy on bass.  Typically it will follow the intro in genres like dubstep and repeat at various intervals.  Sometimes it will be during chorus like in the pop song "Too close".  The exact sound varies and has evolved over the years from extreme sub-bass wobble bass to more screeching FM synthesized bass at a higher frequency.  The examples given should give you and idea of the various ways a "drop" is implemented.
 
Sine waves are not typically used for this sort of thing except for the general adding weight to the bass you described.  Most bass of this type is typically done with saw or square waves or some combination of waves with lots of dynamics since it will be heavily filtered.

Considering the OP mentioned his son wants to add some bass drops to a metal song he's working on, I am nearly positive (short of a direct confirmation from the OP) that he's referring to the effect that I linked examples of in my last post (sometimes referred to as "sub drops" and other unofficial names). That deep, one-shot BOOOOOOM sound. If your a regular listener of metal, you know exactly what he's referring to when he says "bass drops" as related to this genre. You're guaranteed to hear at least half a dozen at any run-of-the-mill metal show at your local night club. Clarification from the OP would be helpful though! *hint hint* ;)
 
But again, it's beyond me (thus far) exactly how the pro's create the effect. I've asked several in the past, and never gotten any reply on the matter. Trade secrets, apparently!

Exactly dimelives1.  I was thinking about recording a "drop" old school style with a bass guitar and working with some octave sort of effects. I think it might be more original sounding than copying sounds from the herd

dimelives, thanks for clearing that up.  I have to listen to your examples on something other than my laptop or cellphone speakes because I don't really hear anything.  I suspect it may be beyond the range of these speakers so i will listen later.  I don't listen to enough metal to know what to listen for.  I do remember dimebag Darrell, so I'm not totally hopeless lol