CFD overnight financing is the daily charge or credit applied to a leveraged position that is still open at the platform's rollover time. Because a CFD gives exposure to the full notional value while only margin is posted, the rest is effectively funded, and the broker applies a benchmark interest rate plus or minus its own markup to that notional amount.
Long positions on index, share and commodity CFDs usually pay financing; short positions may receive it or pay it, depending on where interest rates sit. The forex equivalent is the swap. Financing accumulates quietly, so it matters far more to swing and position traders than to intraday traders who close before rollover.
Next step
Calculator
Trade Cost Calculator
Add up the spread, commission and overnight swap on one forex trade, and see how many pips it must move before you break even.