Mocking up means creating a preliminary version of something, typically a design or prototype. There are several synonyms for this phrase, including modeling, prototyping, simulating, imitating, and fabricating. Each of these words carries different connotations, but their overall meaning is the same. Modeling suggests creating a three-dimensional representation, while prototyping refers to building a functional version of a design. Simulating implies using software or other technology to create a virtual version. Imitating and fabricating both refer to creating a replica, with imitating suggesting a more exact copy and fabricating allowing for some creative interpretation. Ultimately, all of these synonyms refer to the act of creating a version of something in the early stages of the design process.