dropdown

Most of the time, avoid talking about UI elements. Instead, describe what the customer needs to do. If you must refer to a dropdown menu or list, it’s OK to use dropdown as an adjective. Avoid using dropdown as a noun. (Like as a UI label: Dropdowns.)

Examples
Pick from the options in the dropdown list.

Use the dropdown menu to find the category you want.

See also Describing interactions with UI, Formatting text in instructions, Computer and device term collection