Default value
10
The value of world.fps defines the speed of the world in frames (server ticks) per second. By default this is 10 fps, which is a good speed if all objects move in full tiles. Higher values yield smoother results, but at a cost to performance. Timing of many events may be limited by the system clock, so fps values beyond 40 or 50 may cause unwanted effects like jitter even for projects that are not very demanding in terms of performance.
For projects making use of pixel movement, higher fps is usually desired. 40 seems to be a good value for general use, but in worlds that have a large number of players, you may wish to lower the value and give players a higher step_size per tick instead.
This var exists for convenience; it is calculated by 10 / world.tick_lag. The value of world.tick_lag is actually more accurate, but it is easier to think of world speed in terms of frames per second. The actual tick rate has a resolution of 1 ms.
When reading world.fps, the result is always given as a whole number to gloss over rounding error.
If you set client.tick_lag or client.fps to a value other than 0, you can make the client tick at a different (usually faster) rate.