Definition:
A pop-under is a browser window that opens behind the active window, so it may remain hidden until the person switches, minimizes, or closes the window in front. It is commonly used to display advertising or a promotional page separately from the content that initiated the opening.
It is neither an element embedded in the page nor simply a superimposed pop-up. Opening an independent window depends on the browser, its settings, and the action that triggers it. Blockers may prevent it, particularly when it does not follow a clear user interaction.
How a pop-under works
The site or advertising creative attempts to create a new window through code. It then tries to place it behind the main window or return focus to that window. The outcome is not identical across browsers, devices, or configurations.
- Initial event: The opening may be attempted when a page loads or after a click, although browsers commonly restrict automatic attempts.
- Creation: If the browser permits it, a URL opens in another window or tab according to the available environment.
- Discovery: The person may see it when switching windows, minimizing the current one, or finishing their main browsing activity.
Appearing behind another window does not guarantee that the content goes unnoticed or feels less disruptive. This sense of intrusion depends on expectations, consent, frequency, and how easily the content can be identified and closed.
Differences from other formats
Position and context distinguish a pop-under from other appearance formats. The actual mechanism should be identified before assessing a campaign or a user experience issue.
- Pop-under: Opens a separate window behind the window that currently has focus.
- Pop-up: Opens a window or presents a layer in front of active content, although the term is also used for embedded modals.
- Interstitial: Occupies a large part of the interface or appears between pieces of content within a browsing experience; it does not require another window. See the definition of an interstitial.
An HTML modal belongs to the document and can be managed with the interface’s accessibility rules. A pop-under exists in a separate browsing context, with its own controls, history, and focus.
Uses and measurement
The format has been used in display advertising, affiliate marketing, and offer distribution. Its presence alone does not show that the window was viewed or that the resulting traffic had genuine interest.
- Technical reach: Recording an opening indicates that the browser created the window, not that the person paid attention.
- Interaction: CTR and subsequent events help separate a technical impression from an observable response.
- Outcome: A conversion should be attributed using consistent rules and assessed alongside quality, bounce, repetition, and cost.
Evaluation requires distinguishing openings, windows that were actually visible, clicks, and final actions. Combining these signals can inflate performance attributed to the format.
Risks and limitations
The concealed nature of a pop-under creates problems involving trust and control. Before using one, teams should review the user experience, platform policies, data processing, and rules that apply in each market.
- Blocking: Browsers and extensions may prevent the opening or turn it into a visible tab.
- Accessibility: Focus changes and the appearance of another window can disorient keyboard users or people using assistive technologies.
- Reputation: An unexpected opening may be associated with deceptive practices, adware, or low-quality sites.
On mobile devices, the concept may behave differently because of tab and application management. A technical allowance should not be confused with permission to track, personalize, or store information.
Alternatives to a pop-under
The appropriate alternative depends on the objective and the moment of interaction. In many cases, the message can be presented within the page with greater transparency and understandable controls.
- Embedded banner: A banner occupies a defined space without creating another browser window.
- Accessible modal: An in-page layer can provide a visible close control, focus management, and context-based activation.
- Voluntary destination: A link or call to action lets the person decide whether to open an offer or additional content.
Comparing these options requires measuring not only immediate response but also abandonment, complaints, and action quality. A pop-under is an opening mechanism, not a guarantee of attention, acceptance, or advertising performance.