Actuarial gains and losses
From ACT Wiki
Pensions accounting.
Changes in actuarially calculated pensions deficits or surpluses over time arising from either or both of:
1. Differences between the actual events as they have turned out and the assumptions that were made as at the date of the earlier actuarial valuation. (Also known as experience gains and losses.)
2. Changes in the actuarial assumptions over time.
See also