slot - HTML: HyperText Markup Language

mdn slot The slot property of the Element interface returns the name of the shadow DOM slot the element is inserted. An element with a slot attribute is assned to the slot created by the slot> element whose name attribute's value matches that slot attribute's value.

mdn slot link alternatif, 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.