Traversable is the root of the collections' hierarchy. In Traversable, there are definitions for a wide range of operations that the Scala Collections API offers. There is only one abstract method in Traversable, which is the foreach method.

def foreach[U](f: Elem => U): Unit

This method is essential to all the operations contained in Traversable. If you have studied data structures, you will be familiar with traversing a data structure's elements and executing a function on each element. The foreach method does exactly so that, it traverses the elements in the collection and executes a function f on each element. As we mentioned, this is an abstract method and it was designed to have different definitions according to the underlying collection that will make use of it, to ensure highly optimized code for each collection.