shadowing

Declaring a new variable with the same name as an old one.

Shadowing declares a new binding with an existing name, hiding the old one; the new binding may have a different type.

Examples

let price = 20; let price = price * 2; let price = price + 5; ends with price equal to 45; each let makes a new variable.
let tag = tag.len(); reuses the name tag for a usize, which let mut could not do.