Explain 'Variance' (Covariance and Contravariance) in TypeScript.

Variance describes how subtyping between complex types relates to subtyping between their component types.

In TypeScript, most types are 'covariant' (e.g., if Dog extends Animal, then Array<Dog> is a subtype of Array<Animal>). However, function arguments are 'contravariant'. This means a function that accepts an Animal is a subtype of a function that accepts a Dog, because the Animal-accepting function can safely handle anything a Dog-accepting function can. Understanding this is crucial for writing safe generic interfaces and complex function overloads.