A milestone like "Coding 50% completed" is poorly defined because it is ambiguous and difficult to measure precisely. Here’s a detailed explanation:

Ambiguity: It is unclear what 50% completion means – is it 50% of total lines of code, 50% of modules, or 50% of functionality?

Measurement Challenges: Determining exact percentages of completion can be subjective and inconsistent.

Milestone Criteria: Good milestones should be clear, measurable, and verifiable. "Coding completed for module X" is more specific and measurable.

Project Tracking: Poorly defined milestones can lead to confusion and inaccurate tracking of project progress.

References:

"Software Project Management" by Bob Hughes, Mike Cotterell, and Rajib Mall.

"The Art of Project Management" by Scott Berkun.