Metal ice pick. Joe Haupt / flickr / 2013 / CC BY-SA 2.0
An ice pick for home culinary use is a tool used to shatter pieces of ice off from a larger piece of ice, or separate ice cubes that have frozen together.
There are a few different designs.
The standard one looks like a large awl — a single metal pointed thin rod coming out from a handle, that you hold in your clenched fist and stab the ice with. The handle may be metal or wood. This design is a classic feature in horror movies.
Another kind looks like a large fork-like gardening implement, with 5 to 6 sturdy tines coming out of it.
On both designs, the handles are quite sturdy, and somewhat weighted, to help you build up momentum.
Metal ice pick. Joe Haupt / flickr / 2013 / CC BY-SA 2.0