Cash flow hedge accounting is the accounting method applied to a cash flow hedge, and that entry explains how such hedges work, what they protect and how they are designated. This page describes the accounting side the longer term refers to.
Under general hedge accounting rules in IFRS 9 and US GAAP ASC 815, a company that uses a derivative, such as an interest rate swap or currency forward, to fix the cash flows of a floating-rate loan or a forecast purchase would otherwise report the derivative's swings in profit immediately. Cash flow hedge accounting instead records the effective part of the gain or loss in other comprehensive income, building up a cash flow hedge reserve in equity, and moves it into profit when the hedged cash flow affects earnings. This matches the timing of the hedge with the item it protects.
The names differ because "cash flow hedge" describes the economic relationship and the designation, while "cash flow hedge accounting" refers to the bookkeeping that follows. To qualify, the company must document the hedge at inception and show an economic relationship between the hedge and the hedged item. Under IFRS 9 any ineffective portion goes straight to profit, while US GAAP, since its 2017 amendments, generally records the whole change for a highly effective hedge in other comprehensive income. Testing is covered under hedge effectiveness.