If you request just a piece of fried fish at a restaurant, rather than the fish platter that includes French fries and coleslaw, you can say you ordered a la carte, or a single item from the menu.
When a restaurant offers separately priced items, you can describe its menu as a la carte. Ordering this way is also a la carte, like choosing individual pieces of sushi instead of an entire platter or meal. The literal meaning of the French phrase is "by the card," although it's used in both languages to mean "according to the menu." The opposite of a la carte is a table d'hôte, or "meal served at a fixed price."