Symbols are unique identifiers:
const id1 = Symbol("id")
const id2 = Symbol("id")
console.log(id1 === id2) // false (always unique)
Even with the same description, each Symbol is different. Symbols are used as property keys that won't accidentally collide with other properties.
You won't use Symbols in everyday code. They're for library authors and advanced patterns. But knowing they exist helps when you encounter them.