I'm not a pension expert, but I will do my best.
Really, it is the accumulation of.... Let me back up. Pension liabilities are very complex and long-term liabilities. In order to determine the value today—and in this case at March 31—of this very long-term liability, actuarials get involved. They include a whole bunch of assumptions about demographics, how long people will live, the economy and inflation. There are tons of input. Every year, that fluctuates, and as those fluctuations happen, those are the actuarial gains and losses that are reflected in the liability.
They are then, under public sector accounting standards, deferred and sort of amortized over time into the accounts. It is just a way of sort of present-valuing the long-term liability into today's dollars.