What is a mockup? I've heard it may be coded how is it possible?

Typically mid to high fidelity, mockups reflect the design choices for color schemes, layouts, typography, iconography, the visuals of navigation, and the overall atmosphere of the product. Coded mockups are an efficient way to save time and resources provided you’re technically confident. There’s also no surprises later on — if a visual element cannot be created in code, it is simply fixed right then and there. Unless you’re extremely proficient, you’ll likely be able to explore more concepts in a specialized tool than in code.