What's an increment?

The term "Increment" is used to refer to the product under development. Product Backlog Items represent work "needed to improve the product". When a Product Backlog Item is Done, "an Increment is born".

Since creating a development plan or a mock-up doesn't (usually) improve the product, the end result of a Product Backlog Item wouldn't be to create a development plan or a mock-up. However, a development plan could help the team create working agreements, including the Definition of Done. Mock-ups can help the team understand and refine the work described in a Product Backlog Item.

I would suggest that the outcome of Sprints shouldn't be roadmaps or tools. Instead of focusing on roadmaps, I'd recommend focusing on an ordered and well-refined Product Backlog containing Product Backlog Items that represent some aspect of a product that is useful to stakeholders. Your first Sprints, much like your later Sprints, deliver these Done Product Backlog Items (and therefore product Increments) that stakeholders can inspect, give feedback on, and perhaps even use.

If I refer to the Scrum guide, an increment is a concrete step towards the product goal. In my opinion, this means that any type of work done by the Scrum team can be an increment, such as a mock-up or a deployment plan or anything else. 
However, when I read: "In order to provide value, the increment must be usable", I wondered if "usable" referred to the customer.

The Scrum Guide says: "Empiricism asserts that knowledge comes from experience and making decisions based on what is observed".

The "mock-up" or "deployment plan" you mention sound more like ways of deferring or avoiding empirical observation. Companies can be quite inventive at finding ways of kicking the can down the road before empirical outcomes are obtained.

Thanks Thomas and Ian for your help. 
I have a better understanding of what can be considered an increment.

I'm going to start my project in a different way. We're going to focus on a scoping that will enable us to build a product backlog to start a first sprint that will enable the delivery of a piece of product. 

@Alexandre Carnelos you might need long Sprints at the beginning, if the team cannot produce the Increment in short periods at this time. Scrum allows for month-long Sprints. 

Hey Alexandre, 

It may be worth checking out Scrum.org’s learning series section to learn more about Increments and other Scrum related topics. They go into more detail then the guide, and often include some details about common myths and misconceptions. 

https://www.scrum.org/learning-series/increment/

Hey Alexandre, 

It may be worth checking out Scrum.org’s learning series section to learn more about Increments and other Scrum related topics. They go into more detail then the guide, and often include some details about common myths and misconceptions. 

https://www.scrum.org/learning-series/increment/

What is the Increment in Scrum, and how does it relate to the Definition of Done, Product Backlog items, and the Sprint Review process?