Iterator
In plain terms
A pattern for sequentially accessing a collection's elements.
Going deeper
The Iterator pattern provides a standard way to traverse a collection without exposing its internal structure. It abstracts iteration.
Under the hood
Built into most languages (for-each, iterators/generators); decouples traversal from the collection.
Examples
for-each loops, Python iterators, generators, traversing trees/lists.
Think of it like...
Like a tour guide walking you through exhibits one at a time without revealing the floor plan.