Phoronix: Debian 6 Will Be Maintained Under An LTS Flag
Debian developers have announced today that Debian 6 will be maintained as a long-term support (LTS) state until February of 2016...
You can call it 3+2(?) years . That Long Term Support is extended or better to say extendible support period, because it depends on varios factors, but mostly that depends on independently dependant supported support - so depending on how these things goes that can be 2 years more or Zero years more .
It's explained really well by this:
The advantage to business is that you could jump forward two releases at a time, half as often. (Some people do that anyway even without security support... and I really should replace that etch server now).