Seed
The starting number for a random generator; the same seed always gives the same result.
See it in Noise & texture. Change Seed and watch the whole pattern change; set it back and the first pattern returns.
In plain words
Random patterns in a computer come from a recipe that starts with one number. That number is the seed. Keep the seed, and the pattern comes out the same every time. Change it by one, and you get a completely new pattern. Sharing a seed is how people share an exact random result.