Diesel Particulate Filter (DPF)
Diesel Particulate filters (DPF) catch bits of soot in the exhaust.
As with any filter they have to be emptied regularly to maintain performance. For a DPF this process is called 'regeneration' – the collected soot is burnt off at high temperature to leave only a tiny ash residue.
If you think your vehicles DPF requires a regeneration speak to your local Ford Dealership.