Lines of longitude get closer together as you approach the poles: lines of latitude are parallel.
The metre was originally defined as one ten-millionth of the distance from the pole to the equator, so one degree of latitude equates to 10,000,000/90 metres or 111.111 km.
If you prefer imperial measure, the nautical mile is defined as 1 minute of arc (1/60 degree), so 1 degree is 60 nautical miles.
Both figures approximate, as the Earth is not a perfect sphere.