They are for anyone. Its basically anything you want to contribute over the minimum that your employer requires. Mine contributes 6% as long as you contribute 2% from your salary. But you can contribute more if you want, so its a voluntary contribution, or AVC beyond the 6+2. Which is pretty low I guess, so at the moment I contribute another 4% and aiming to up that as soon as I can. There is a limit you can put with tax relief which depends your age and there is a table somewhere.