A manual post-hole auger is a metal bar with a large metal thread at one end which works like a screw to drill into soft ground…
…to create a hole for a fence post.
It has a T-shaped handle so it can be turned by hand.
A manual post-hole auger is also known as a post-hole digger or post-hole borer. Be careful though, there are other tools known as post-hole diggers so you may need to double check which one a manufacturer is referring to.