Conversion Tracking
Conversion tracking is the mechanism that records what happened after someone clicked your ad - a form submitted, a call placed, a purchase made - and reports it back to the ad platform.
Why it matters
Without it, every optimisation decision in an account is made on clicks. Clicks and jobs are not the same thing, and the gap between them is where advertising budgets disappear. A campaign producing expensive clicks and cheap jobs looks like a failure; one producing cheap clicks and no jobs looks like a success. Conversion tracking is what tells those two apart.
What people get wrong
That having a tag installed means it is working. A tag can sit in an account for years, appear perfectly configured, and never fire once - because a form's success URL changed, a trigger condition broke, or a consent banner blocks it. Installed and firing are different questions, and only one of them matters.