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The most basic interface for all collections in most programming languages is the Iterable interface (or its equivalent), which allows iterating over the elements of the collection.

For example, in Java, all collections implement the Iterable<T> interface, which defines the iterator() method. Thanks to this, a for-each loop can be used to traverse the elements of any collection.

Example in Java:

List<String> list = Arrays.asList("a", "b", "c");
for (String item : list) {
    System.out.println(item);
}

Thus, the Iterable interface provides the basic functionality for traversing elements, upon which more specialized collections are built.