What is damascus steel? Damast / damascus / folded steel

What is damasteel (also called damast, damascus or folded steel) and does it have added value?

What's the Deal with Damascus Steel?

Boker MG-42 Sherman Damascus Dagger – Kaviso

Damascus Steel Folding Knife - Pocket Knife - FK08 - Craftomatik

NedFoss Griffin Damascus Pocket Knife, VG10 Damascus Steel Blade

Boker Plus P-51 Mustang Damast Studded Metal Design Titanium

Scythian Handmade Damascus Steel Knife – Forseti Steel

Boker Mokume Walnut Damascus Knife

Damascus Steel - The Truth About Folded Steel Katana

Damascus blade folding knives