What type of estimates can be considered 'conceptual' or 'ballpark'?

The option that accurately represents estimates considered 'conceptual' or 'ballpark' is indeed the Order of Magnitude Estimates. These estimates are typically used in the early stages of project planning, often before detailed requirements and specifications are available.

Order of Magnitude Estimates provide a rough approximation of the project's cost, usually within a margin of error of -25% to +75%. They are instrumental in helping stakeholders make preliminary decisions about project feasibility and budget allocation without the need for extensive data collection or analysis. By serving as preliminary figures, they assist in guiding discussions about project scope, priorities, and the potential financial investment needed.

In contrast, Definitive Estimates are much more accurate and based on detailed project information, while Budget Estimates offer a more refined figure derived from historical data and preliminary project parameters. Contingency Estimates specifically allocate reserves for unforeseen costs. Therefore, the Order of Magnitude Estimates stand out as the most appropriate term for conceptual or ballpark figures in the realm of cost estimating.