String trimmer
Also called: weed eater, weed whacker, line trimmer, strimmer
A handheld tool that cuts grass with a spinning nylon line, used for edges, fence lines and around obstacles a mower can't reach. Also called a weed eater or weed whacker. Gas or battery, $100–$200.
The mower does the bulk of the lawn; the string trimmer does the edges people actually notice — along fences, walls, beds, posts and tree trunks. Trim first and mow second, so the mower picks up the trimmings.
Battery trimmers ($120–$200) have replaced gas for most homeowners: no mixing fuel, no pull-starting, less noise, and enough runtime for a quarter-acre lot on one charge. Gas ($120–$250) still makes sense for large properties or heavy brush.
Two habits: keep the head level (tilting it scalps the grass), and keep the line away from tree trunks — a trimmer can girdle the bark of a young tree and kill it in one season. Trimmer line is a consumable, about $15 a season.
A related tool, the edger, uses a vertical steel blade to cut a clean line where lawn meets sidewalk or driveway. Many trimmers rotate 90° to do a rough version of this.