Campaign is the top-level advertising structure where objective, budget, targeting, bidding, and settings are usually defined.
It matters because paid search can spend budget quickly. Knowing this term helps teams control intent, targeting, bidding, creative, conversion tracking, and lead quality instead of optimizing for surface-level clicks.
Example
An HVAC business separates repair inquiries from new-system installations into different campaigns because their budgets, destinations, and commercial priorities differ. Each campaign can contain more focused ad groups without forcing both services to share every spending and bidding decision.