For tax years before 2016/17 this was the amount of pay beyond which you ceased to pay the lower contracted-out rate of national insurance contributions.
The upper accruals point for 2015/2016 was £770 per week.
On earnings above the upper accruals point and up to the upper earnings limit of £815 per week in 2015/16 the full 12% national insurance contribution was payable.
On earnings above the upper earnings limit a 2% national insurance contribution was and is payable.
On anything you earn over the upper earnings limit, you only pay 2% national insurance contributions. The upper earnings limit for 2017/18 is £45,032 pa.