Walled garden

A platform — like Meta, Google, or Amazon — that lets you advertise and measure results inside it, but won't let raw user-level data out.

Example

You can see aggregate campaign performance inside a platform's ads manager, but you can't export the underlying user-level exposure data to combine with your own independent measurement.

Why marketers care

It's a big part of why independent, cross-platform measurement — like MMM, or a third-party brand lift study — exists at all. Walled gardens each grade their own homework, and a customer often wants a read that isn't graded by the platform being measured.