In restaurants, à la carte  is the practice of ordering individual dishes from a menu in a restaurant, as opposed to table d'hôte, where a set menu is offered. It is an early 19th century loan from French meaning "according to the menu".
The earliest examples of à la carte are from 1816 for the adjectival use ("à la carte meal", for example) and from 1821 for the adverbial use ("meals were served à la carte"). These pre-date the use of the word menu, which came into English in the 1830s.
More broadly, the term is not exclusive to food. Today, it can be used in reference to things such as television. To watch television à la carte refers to paying for a provider where the viewer can choose from an option of programs to watch (e.g., Netflix or Hulu), instead of watching from set programs.