what's the ";Send"; on a VDL 2.5 instrument in Kontakt 4.....";send";ing to?

NOTE: The numbers in parentheses refer to the numbers in the attached image.

I'm presuming you're referring to the Aux Send sliders (1) that are under each instrument. That allows you to send some of the audio signal for that instrument to one of the Aux Return strips (2) located in the Output area (3). For them to work you'll need to make sure that the Configuration (4) at the bottom of the Aux Return strip you plan on using is set to be output to your sound card.

These basically allow you to apply effects in groups. Say you want to add reverb to just a single instrument or groups of instruments; this function in Kontakt or Kontakt Player allows you to do that.

Bryan, thanks for your quick reply!
No, actually, I was referring to the large ";Send"; knob, just to the right of the ";Virtual 2.5"; logo on the instrument, but I think your photo has answered my question! It seems that it's ";send";ing to the K4 mixer Aux 1, am I correct?

Yes, you are correct.

I just read too quickly and got ahead of myself. While we're on the subject though, you can have up to four different sends, as you could see from my little visual aid.