I got a question for you: The Project Management Triangle (called also the Triple Constraint, Iron Triangle and "Project Triangle") is a model of the constraints of project management. While its origins are unclear, it has been used since at least the 1950s. It contends that:

Based on this passage, what is the iron triangle in project management?
Let's think first:
To answer this question, we should know that: The Project Management Triangle (called also the Triple Constraint, Iron Triangle and "Project Triangle") is a model of the constraints of project management.
Therefore, the answer is a model of the constraints of project management.