As of now, there are a considerable number of volumes of the Overlord light novel. But the exact count might change over time as new ones are released.
The Overlord light novel has multiple volumes. The series has been ongoing and new volumes are added over time. To get the precise number, you might want to look at the publisher's website or search for the latest updates from reliable sources in the fan community.
Perhaps the story takes a different turn in terms of the main character's goals. In previous volumes, he might have been focused on one aspect of building his power, but in Vol 11, he could be branching out into new areas. So, the direction of the plot is different.
Again, not having read it, it's hard to say precisely. But usually, the story in Overlord progresses by building on the previous events. If in the previous volumes Ainz was establishing his base, in Vol 17 he might be moving towards more outward expansion or dealing with the consequences of his earlier actions.
The number of volumes of Overlord manga varies depending on the latest releases. Currently, I think it's approximately 14 or 15. Keep an eye on the official sources for the most accurate and up-to-date count.
Yes, 'Overlord' is a light novel. It has an interesting premise where the protagonist gets trapped in a virtual world that he has to rule. It's been adapted into an anime as well.