This concept generally arises when forward hedging takes place as these are popular to arrest rate risks, Forward delta conventions are normally used to specify implied volatilities because of the symmetry of put and call deltas adding up to 100%. Using forward deltas as a quotation standard often depends on the time to expiry T and the presence of an emerging market currency in the currency pair.
If the currency pair does contain an emerging market currency, forward deltas are the market default. If the currency pair contains only currencies from the OECD economies (Organization for economic cooperation and development) (USD, EUR, JPY, GBP, AUD, NZD, CAD, CHF, NOK, SEK, DKK, PLN) then spot deltas are used out to and including 1Y.
For all longer dated tenors forward deltas are used. An example: the NZD-JPY uses spot deltas for maturities below 1 year and forward deltas for maturities above 1 year. However, exotic pairs like CZKNZD uses forward deltas.
