Detailed plan describing objectives and activities involving promotions to achieve objectives set in the marketing plan.

A promotion plan outlines the promotional strategies that may be used to achieve the marketing objectives.

A promotional plan is only one component of a marketing plan, covering all types of communication between the seller  and potential clients. There are four basic components of a promotional plan: Advertising, Personal Selling, Sales Promotion & Public Relations.

See also:
Marketing plan
Advertising
Sales promotion
Public relations
Direct marketing
Packaging