Revision or alteration of rules, fees, systems, etc.; often used when policies or numerical values are changed (overlaps with 改訂 in some contexts).
会則が改定され、会員の年会費が上がった。
The bylaws were revised and the members' annual fee was raised.
料金改定は来月から適用される予定だ。
The rate revision is scheduled to take effect from next month.
この規定は時代に合わせて改定する必要がある。
This regulation needs to be revised to suit the times.