Answer

Covariance allows you to use a subtype in place of a supertype. In Kotlin generics, it is denoted by the `out` keyword.

Producer (out)

• If a generic class only returns (produces) type T, it can be covariant.
• `List<out T>` is covariant. A `List<String>` IS A `List<Any>`.

```kotlin val strings: List<String> = listOf("A", "B") val objects: List<Any> = strings // Valid because List is covariant (out T) ```

Contravariance (in)

• If a generic class only consumes type T, it is contravariant.
• Denoted by `in`.
• `Comparable<in T>`. A `Comparable<Any>` can compare Strings.