wpsnoop [list-double-optin-link] shortcode is used by 3 plugins

WordPress Shortcodes are used to create visual effects like [bold] text [/bold]

Shortcodes can also be used to embed Videos, Calendars, Tables, Products, Product Reviews, GitHub badges, source code, almost anything - and therein lies the great benefit of WordPress shortcodes and also the problem of conflicting plugins competing to try to make [list-double-optin-link] a shortcode appear on a page.

This page provides some information on the list-double-optin-link shortcode and a list of plugins and themes that implement it.