Literally 'legs', usually made of nioi, which extend from the hamon to the cutting edge.

There's been an opinion that ashi was developed consisting of softer steel within the yakiba to localize the breaks and prevent the blade to be broken in half. When stress is applied to a section of the blade, the blade would chip at the harder areas because the ashi around it would absorb the stress.

An example of ashi can be seen here: Hataraki @

Types of ashi

ko-ashi - small ashi.
nezumi ashi - 'Rat's feet'. Small numerous ashi.
choji ashi - clove-shaped ashi.
gunome ashi - zigzag-shaped ashi.
saka ashi - slanted ashi.