What do you call a menu that expands as you move through the site?

Question

On web sites, I often find a menu, usually on the left-hand side of the page that expands as I traverse through the site structure. For example, if I was on a top-level page, I might see the following:

Top-Level Page A
Top-Level Page B
Top-Level Page C

If I click onto Top-Level Page C, I may then see the following:

Top-Level Page A
Top-Level Page B
Top-Level Page C
- Second-Level Page A
- Second-Level Page B
- Second-Level Page C

As I continue to traverse, the menu changes. Is there a name for this?

Answer 1

The interaction style is accordion and the structure of the menu is tree style.

Answer 2

I'd like to know if there's an actual name for this, but depending on the actual intent of the design, you might call it one of several different names.

The first one that comes to mind is a more generic name, something like a 'reactive' or 'responsive' menu, because it reacts or responds to where you are in the site to show you the options available.

Alternatively, you could also call it an 'adaptive' navigation, which is probably a fancy name for a vertical rather than horizontal breadcrumb that gives you the point of reference within a website. Then there's probably combinations of the two that I mentioned.

However, it would be interesting to know how many levels of depth this menu actually goes into, because one of the limitations of such a design is the complexity of the website in terms of deeply nested pages. I daresay that being a vertical menu it doesn't have enough horizontal space to do this, so I would be curious to see an actual example.