Feather
Feather turns up in 2 fields: welding, asphalt. Here is what it means to the people in each one.
Feather in welding
To grind the start, stop or tack of a weld to a thin taper so the next bead can tie in smoothly.
Grinding a weld end, tack or crater to a gradual taper with a disc or file so the following bead melts through it instead of piling up against a blunt edge. Feathering root starts and stops and tack edges prevents cold lap, lack of fusion and incomplete penetration at tie-ins, which are some of the most common spots for radiographic rejects.
"Feather every tack and both ends of the root before you hot pass it."
Feather in asphalt
To taper new asphalt down to nearly zero thickness to tie it into an existing surface.
To thin a mat out to a fine edge where it meets a gutter, driveway, existing pavement or structure. Feathering avoids a lip, but the thin edge cannot hold coarse aggregate or reach density, so it tends to ravel and peel. On quality work crews mill a butt joint or keyway so the new mix ends at full depth instead of feathering out.
"Don't feather it onto the concrete apron, sawcut and mill a butt joint or it'll be gone by spring."