Difference between Project Plan and Work Plan

Guys,

I am new to project management and frequently need to create IT proposal documents for client RFPs with project plan. But recently i was asked to give work plan and then project plan in two different sections of the same RFP, my understanding was they were both the same and every time I get this question it puts me in a swing.

Below is what the client is asking for in their words but the work plan details are asked under the section "Project Approach/Management" and project plan details are asked under the section "Project Plan" :

Project Approach/Management:

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Describe your Initial Work Plan and schedule, including a detailed timeline and milestones for all Phases of the project.

Project Plan:

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Develop a project plan with dates and milestones to be used throughout the project.

I usually do 1 plan ( call it project or a work or implementation plan ) in an excel document with tasks, timeframe, resources, deliverable, milestones. Now that RFP requires work plan & project plan in 2 different section there has to be some difference. Can someone shed some light how the "initial work plan & schedule" is different from "project plan" IN THIS CONTEXT?

Thanks in advance, any help is appreciated.

Chris