Flint, a basic crafting resource used to make arrows, spears, upgrade craft bench, etc. in Valheim. It is required to build a chopping block.
Flint locations: Where to find Flint
Flints stones are found near water bodies. To easily spot Flint, look out for elliptical-shaped light grey-colored stones near water shores. Go close to the stone and if it is Flint, you should see the name pop up for it.
Below are few images for reference.