They are officially known as string trimmers. Where are you geographically and what do you call them?

Grew up in New Jersey and we called them weed wackers.

we call them weedeaters in Tejas

In western Canada we either call them weed whackers or whipper snippers.

Australia calls them whipper-snippers.

UK - Strimmer (contraction of string trimmer I guess, but never though about it till today)

Florida: weed eater or weed whacker. I have also heard grass whip.

Weed yeeter. Southeast US.

I've heard "weed whackers" and "strimmers" down in Florida.

Alabamians call them weedeaters. Wedeeters.