What is interleaving?

Something of a newbie but what is it, why is it used, how can I tell if I have it and would I be better off without it.

Many thanks in advance

Here is some info Mr Saffron put in his faq:
Many people buy a faster ADSL service thinking it will improve their gaming latency/ping, this is not correct. Your latency is relatively fixed according to the settings used by your network provider, and which ADSL service they are using, e.g. BT Wholesale based, or an unbundled service. The Max products will allow you more upstream bandwidth which will be welcome for people hosting their own games servers as more people will be able to use it, plus for those games that use audio and video streaming you may see an improvement.

One warning. The Max products are intended to give the fastest posssible line speeds, and to this end an error correction technique called Interleaving may be switched on for an individuals line. Interleaving improves the error correction, and may give you more download speed but at the expense of 20 to 40ms of latency, ie. no good for gamers. BT Wholesale is exposing the ability to the service providers to turn off this feature for an individuals line, so if you are a gamer you may have to sacrifice perhaps 10% of your line speed to get a lower latency. Most ADSL modems will report whether they are using FAST mode (the current connection method) or Interleave mode, so you can tell if your latency suddenly jumps, whether it is the line or possible the service provider re-routing your data.

jimmy