Frames per second

Frames per second (short form FPS) is a number of frames per one second.

Description
This is the number of the frames (or game updates) per second. So if the player has 10 FPS, the game will update every 0.1s (100ms). However, if the player has 40 FPS, the game will update every 0.025 seconds. Bigger value of FPS means a smoother game with lower cases of lags.

Minecraft FPS
In Minecraft, you can differentiate 4 groups based on their FPS:

Insufficient (0 - 10 FPS)
The game will go slow, it can crash and also kick a player from the server. It is insufficient, so you can only install some mods, that give more FPS.

Sufficient (10 - 60 FPS)
The game will be normal, but you won't be able to run any other extensions or mods. It is better to clean some space on the computer and have OptiFine.

Normal (60 - 500 FPS)
The game will be normal and you will be able to install more mods. The game will run smooth and you can more graphically improve Minecraft instead of improving performance of Minecraft.

Extreme (More then 500 FPS)
The game will be running very well, so smooth and you will be able to install mods. You can install HD textures or shaders without a big performance difference.