slot - HTML: HyperText Markup Language

mdn slot A named slot is a slot> element with a name attribute. Example. Let’s make an example using the slot> element along with the template> element. Partnering slot> with. Slots are identified by their name attribute, and allow you to define placeholders in your template that can be filled with any markup fragment you want when the element is used

mdnslot, The slot property of the Element interface returns the name of the shadow DOM slot the element is inserted.