From Minecraft Wiki

A tick is one cycle of the game loop.

Game tick

The game loop runs at 20 ticks per second, so one tick counts as 120 of a second, or 0.05 seconds. An in-game day lasts 24,000 ticks or 20 minutes. Ticks do not affect the game's FPS (frames per second).

Chunk tick

On every game tick, all chunks within the render distance of a player and within 128 of a player are ticked.

This can have various effects such as:

  • During a thunderstorm, lightning will strike somewhere in that chunk (1100000 chance).
  • 116 chance that one column of the chunk is chosen for weather checks on the topmost block.
    • If the chunk is in a cold biome, water freezes into ice.
    • If it is snowing in the chunk, a snow layer is placed.
    • If it is raining in the chunk, a cauldron is filled.

Block tick

Chunks are split into 16 sections, each one a 16×16×16=4096 block cube. On every game tick, three blocks (or whatever /gamerule randomTickSpeed is set to) are chosen from each section in the chunk. The chosen blocks are given a "block tick." Various things can happen, like crops growing, fire spreading, ice melting, etc.

Since block ticks are generated randomly, there is no way to predict when a block will receive its next tick. The median time between block ticks is 47.30 seconds in Java Edition, and 141.94 seconds in Bedrock Edition. The average time between block ticks is 68.27 seconds in Java Edition, and 204.8 seconds in Bedrock Edition.

Redstone tick

A redstone tick spans the length of two game ticks, so one Redstone tick counts as 110 of a second or 0.1 seconds. By default, a redstone line doesn't take any time to travel, but a redstone repeater increases the delay by 1–4 ticks, depending on what it is set to.