A menu is a list of the food that's available to order. If your vegan friend doesn't see anything on the restaurant's menu he can eat, you may have to ask the chef to make him something special.
A menu is a list of what's available, whether you're talking about a menu at your neighborhood cafe or the menu, or agenda, of things to do at the state fair. When you talk about a menu on your computer, you're also talking about a list — in this case, a list of options or commands on the computer screen. Menu comes from the French phrase menu de repas, "list of what's served at a meal."