A lead's first funding of their account with the advertiser — the billable event for most financial and crypto offers.
FTD (first-time deposit) is the moment a delivered lead deposits money with the advertiser for the first time. In finance, forex and crypto verticals the FTD, not the registration, is the action that triggers payout, which is why these offers are described as paying "per FTD".
Because an FTD can arrive hours or days after the lead is delivered, it is reconciled asynchronously: the advertiser reports it via postback or status API, and the affiliate's ledger moves the record from pending to a billable state.
In d0pe an FTD is recorded as a deposit held in the ledger until reconciled; on approval a server-to-server postback fires to the traffic source carrying the payout.