What is the tick speed in Minecraft?

The question is already below, so I always play Minecraft and when setting the worlds there's always this field at the bottom where tick speed is and you can write a number or something, but I don't know what that is.

I think that means it indicates game speed. That is, a higher tick speed indicates how quickly trees grow, days and nights pass, zombies spawn, etc.

As far as I know 10 ticks are 1 second… (is a Minecraft time unit)

Edit: have checked; 20 ticks correspond to 1 second