That's like asking what is the difference between a duck.

Very vague:
Campaign is the overall compilation of strategies. A plan is a strategy...same thing different words.

To me, you have to develop the strategy first. Based on that, you create an action plan to carry out the strategy. The campaign is the execution of the action plan.

The strategy is the goal-- you have decided you want to sell something to a specific groups of customers. Then you develop what actions you will take to make that goal. The campaign is when you pull it all together.

Don't worry about the words-- if you are reaching the customer and sales are up -- your boss won't care about the words you use.

I've been telling my audiences (I am a speaker and author) that most companies and people confuse those words and your question and the answers have just added evidence.
First, you will need to use the words the way your boss does so you can communicate. It is not usually a good idea to tell your boss he/she is wrong about the definitions.

Second, there are steps you want to go through if you want to go 'by the book.'
Have a clear vision: where you want to go but are not there yet.
Have a clear mission: what the company does, how it behaves, who it serves when everything is going right.
Have a few major goals: could be sales numbers, customer satisfaction rates, # of new products to market, market share, whatever is reachable (can be a stretch, but reachable).
Have a few strategies to reach those goals. Strategies are a few sentences at the most about your direction and overall plan to reach your goals.
Finally you put together tactics: detailed plans to implement the strategy and reach the goals. Marketing campaigns are part of those tactics.

There have been some other notes about this in at least one of my blogs. You can check out brainstorming-that-works.com or brainiance.com.

Good luck,
Hazel Wagner

Strategy = the 'what'
Action plans = the 'how'
Campaign = execution of the 'how'

good luck,

ethnicomm inc.