Before the advent of the modern electric refrigerator (and the ready convenience of a tray of ice cubes) people bought ice by the block. The iceman would deliver to your door and put it into an icebox -- literally, just an insulated box which slowed down the melt rate.
You had to conserve it, and needed some way to take small amounts from the block -- that's where these tools came in.
Most are acquainted with the North Bros as makers of those eggbeaters with multiple settings, or perhaps the yankee screwdriver, or my favorite -- the vaunted Yankee bit brace.
That is how I first came to know these devices -- one was marked with the North Bros name and I did a little research.
google "antique ice shaver" and you can see dozens of examples.