There's a common access pattern with object-relational mapping frameworks where an initial query will be used to get a list of ids, then an individual queries are emitted for each item to get the details of the items. For example, if you have a database table full of stories, and you want to see only the stories written by a certain author, it is common for a framework to have a function like

    stories = get_stories(query)

which results in a SQL query like

    SELECT id FROM stories WHERE author = ?

with the '?' being bound to some concrete value like "Jim".

Then, the framework will be used to do something like this

    for id in stories {
        story = get_story_by_id(id)
        // do something with story
    }

which results in N SQL queries with

    SELECT title, author, date, content FROM stories WHERE id = ?

and there's your N+1