At higher AUWs, the ailerons are deflected upwards to move the lateral (spanwise) centre of pressure inwards to take they strain off the outer part of the wing.
Not all aircraft have it. The VC10 was the first to my knowledge, it is simply a switch which moves the ailerons up about 8 degrees. It is switched manually at certain
weights and altitudes.
The Tristar took it a step further with an automated system, and the modern state of the art system is the A330/340s Manouevre Load Alleviation, but someone else will have to explain that.