Most people use the words interchangeably. They should not.
A worry is something that creates anxiety in the person running the project. It is personal, emotional, and often disproportionate to the actual probability of the thing happening. Worries are real. They deserve attention. But they do not belong in a project risk assessment.
A risk is a specific, plausible event or condition that could materially affect the project's outcome. It is structural, not personal. It exists independent of how the owner feels about it. It belongs in the plan.
The confusion between the two produces project planning that is emotionally organized rather than strategically organized. The owner spends time and mental energy on the things that frighten them most, which are not always the things most likely to affect the project.
What This Looks Like in Practice
A trades contractor planning her first product launch might worry constantly about what happens if a large competitor copies her design. This worry is understandable. It is also, for a first product with a small initial market, a relatively low-probability near-term risk. The larger competitor has limited incentive to copy a small entrant until that entrant has proven the market exists.
The risk that actually deserves attention in her plan might be something far less dramatic. Her single manufacturing partner has a twelve-week lead time. If that partner has a production problem during her launch window, she has no fallback. That is a risk. It is not keeping her up at night, but it should be in the plan.
The worry gets the attention. The risk gets ignored. The project suffers for the wrong reason.
The Test
When something surfaces during project planning, apply a simple test before deciding how to treat it.
Ask: is this a statement about how I feel, or a statement about what could happen?
If it is a statement about how you feel, it is a worry. Acknowledge it, set it aside, and do not let it drive resource allocation in the plan.
If it is a statement about what could happen, ask the follow-up: is it specific, plausible, and material? Specific means it describes a particular event, not a vague category of badness. Plausible means it could reasonably occur given the actual circumstances of the project. Material means it would meaningfully change the project's outcome if it did occur.
If it passes all three, it is a risk. It belongs in the plan with a response attached to it.
If it fails any of the three, it is still worth knowing about. But it does not belong in the project risk assessment, and it should not be consuming planning energy that belongs elsewhere.
Worries managed. Risks planned. That is the discipline.