Can someone explain what a minecraft seed actually is?

on Java you can type words in as a seed too, the game just converts the text to a number. so "bob" is a real seed. and since 1.18 java and bedrock make the same terrain from the same seed, structures and some details still differ between them.

it's the number the world generator starts from. same seed on the same version gives you the exact same world, villages and structures in the same spots. that's why people share them.