Number lock

Some keyboards have a number pad: that’s a block of number keys arranged in a grid. If you’re typing a lot of numbers, using these is much more convenient than the row of number keys above the letters.

7 8 9 4 5 6 1 2 3 0 .

Because the number pad keys are arranged in a grid, it’s also a useful layout for the arrow keys.

7 9 5 1 3 0 .

The number lock key lets you switch the number pad’s keys’ behaviour between those two modes. Press it to toggle between numbers (num lock on) or arrows (num lock off).