While learning with Django by Example, I have found something I don't yet know and haven't found any reference for it. I'm sure it is well documented somewhere, but I haven't found out how to search for it. Also, I apologize if I'm reasking an already answered question, I haven't found it here either. 
What I would like to understand is the "admin: ..." syntax, which I met in several contexts:

In a template .html file:

```
<a href="{% url admin:todo_datetime_add %}">Add Todo items</a>

```

In a view function:

```
return HttpResponseRedirect(reverse("admin:todo_item_changelist"))

```

I have gone through the djangoproject tutorial and the first 8 chapters of djangobook, and I didn't meet it there. I know, though, that in a reverse function a view function may be passed, and that {% %} template tags 'do something', but I have only seen dotted syntax used for these cases, so far. May it be that for referencing admin features, instead of the dotted syntax, we use this colon? 
I would really appreciate some brief explanation on what it does, or a reference link would be great, too.
And again, I'm sorry if I'm reasking an already answered question.