Immutability is the quality of being unchangeable. In Scala, variables are immutable by default; once assigned a value they cannot be modified by you or any other programmer. This might not be apparent now, but default immutability is one of Scala’s strongest features. It is primarily used for concurrency control which manages concurrent (simultaneous) operations so that they do not conflict with each other.

You can also create immutable variables by explicitly mentioning it in your code.