A digital marketing campaign is a focused time-bound effort, to achieve specific marketing goals, such as promoting a product, increasing brand awareness, or generating leads.
A digital marketing strategy, on the other hand, is the overarching plan that guides and informs all marketing activities, including multiple campaigns, in order to achieve the long-term objectives of a business.
In simpler terms, a strategy is the broader plan, while campaigns are the individual tactics used to execute that plan.