Lead Magnet
Something of real value, a guide, discount, template, or tool, offered for free in exchange for a visitor's email address.
A lead magnet is the trade at the center of every popup: the visitor gives up their email, you give them something worth more to them right now than their privacy is worth to keep.
The strongest lead magnets are specific to the page they appear on. A generic "Subscribe to our newsletter" popup converts far worse than a checklist, calculator, or discount tied directly to what the visitor was already reading or shopping for.
A lead magnet without a fast follow-up is wasted. Whatever you promise should arrive within seconds, either instantly on-screen or in the first email, or the trust you just built evaporates.
See it in practice