What is the difference between popover menu, drop-down menu & fly-out menu?

Dropdown refers to the visual effect of the menu opening. So all menus dropdown but the term is generally used for keyboard and mouse menus (desktop) as opposed to touch menus. Popover refers to the visual effect of the menu appearing on top of everything visually. So all menus popover.

1. What is the difference between pop up and drop-down menu?
2. What is a popover menu?
3. What is a dropdown menu?

What is the difference between pop up and drop-down menu?

A pop-up list lets the user choose one option among several and generally displays the option that was last selected. A pull-down list is generally used for selecting commands in a specific context.

What is a popover menu?

A container that opens when the user taps an element or a region. You can use it to provide contextual information or options.

What is a dropdown menu?

A dropdown menu is a list of options on a website that appears only when a user interacts with the menu, like by clicking on it or hovering over it.