A custom widget is an additional function or service you can add to your retarget link page. It can be a curated page, bio link page or just any other curated content page. All you need to do is embed the script and it will appear on your page.
You can add your chatbox / offers / services to other's blog posts
You can integrate your newsletter popup form to other's blog posts
Use forms for data collection
Add gifs or videos for user knowledge
Use countdown timer announcement of an event
Use spin wheels for any kind of lottery game