When you play online, your screen shows a smooth picture, but the server, the computer that decides what really happened, does not watch the match like a film. It works in steps. Many times a second it reads everyone's inputs, moves the players, checks for hits, and writes down the new state of the match. Each of those steps is called a tick.
The tick rate is how many ticks happen per second, measured in hertz (Hz). A server at 64 Hz makes 64 steps every second. A server at 20 Hz makes only 20. Between two ticks, the server knows nothing new.
The time between ticks is simple maths: divide 1000 by the tick rate. At 128 Hz that is about 7.8 ms. At 64 Hz it is about 15.6 ms. At 20 Hz it is 50 ms, which is already as long as a decent ping.
Try it below. The coral dot is a player running at a steady speed. The square outlines are what the server records at each tick. Slide the tick rate down and watch the server's picture turn into a series of jumps.
That gap is the whole story. A player who moves fast and a server that updates rarely means the server's picture lags behind reality by up to one tick, every time.
A higher tick rate shrinks that gap in three ways. The server reads your inputs sooner, so a click waits less time for the next step. It checks hits more often, so a fast player is less likely to slip past a bullet between two snapshots. And it sends updates to your game more often, so other players look smoother and their positions are fresher on your screen.
This is part of why the same shot can feel different in two games. Valorant, for example, runs 128-tick servers, which its makers present as a standard for competitive play. Counter-Strike 2 takes another route: instead of only counting steps, its servers use sub-tick updates that record the exact moment an action happened. Different games make different trade-offs, and many run lower rates to keep servers cheaper.
It is easy to blame the tick rate for everything, but it is only one link in a chain. Your ping (the round trip to the server) usually matters more. If your ping is 60 ms, then going from 64 Hz to 128 Hz saves less than 8 ms of waiting, which is a small slice of the total. Your own screen matters too: a 60 Hz display shows a new picture only every 16.7 ms, however fast the server runs.
A fast tick rate also cannot help if your connection is unstable. Packet loss and jitter (ping that jumps around) make a game feel worse than any tick rate difference. Fix those first.
You usually cannot choose the tick rate. The game's makers set it, and it is rarely shown in the menu. What you can do is act on the parts you control:
Next time someone online says "the tick rate is bad", you will know what they mean: the server is taking fewer snapshots, so its picture of the match jumps further between steps.