Final answer:
The logical relationship between project tasks or between a project task and a milestone is called a dependency.
Step-by-step explanation:
The logical relationship that exists between project tasks or between a project task and a milestone is called a dependency. A dependency represents a sequence or order of tasks in a project, where one task depends on the completion of another. It ensures that tasks are performed in a specific order to maintain project flow and achieve project objectives.
For example, if you have a project task of designing a website, you may have a dependency on the completion of a task for gathering client requirements. The website design task cannot start until the client requirements are gathered. This dependency ensures that the website design task is not conducted prematurely.