Before any line of code is written, there is the pre-development design phase every project usually goes through. That’s when wireframes, mockups, and prototypes are created.
Mockup vs prototype vs wireframe is a subject that needs clarity, as it is seen differently by designers and clients.

This article explains how wireframes, mockups, and prototyping are different and when it’s best to apply them

https://steelkiwi.com/blog/wireframes-vs-mockups-vs-prototypes/

Author's Bio: 

Full-cycle software development service provider
We’ve built a strong team of software engineers, designers, quality assurance specialists, and project managers to provide a high standard of delivery to our clients.

https://steelkiwi.com