Despite its wide usage the word "lemonade" can name rather different drinks in different countries around the world. Nevertheless, a common thing is that all lemonades are made using lemon juice or something that substitutes it. Lemonade is probably the oldest commercial soft drink. Its sales began at least in the 17th century in Paris. In 1676 a business called the Compagnie de Limonadiers had monopoly rights to sell lemonade; salespeople of the company carried tanks with the beverage upon their backs and were serving them in cups right on the street.
In the United States and Canada lemonade is usually a noncarbonated beverage made by mixing lemon juice, sugar and water. If grenadine is added to the drink it becomes pink lemonade which is traditional for the US. Lemonade is usually served with ice and a straw.
In the United Kingdom the drink that is called lemonade in the US is rather uncommon. It is usually called "traditional" or "cloudy" lemonade. Although made similar to the US variation (mixing lemon juice, water and sugar or other sweetener), a lemonade in the UK is a carbonated beverage. A drink called Shandy made by mixing lemonade and beer is also popular in Great Britain (in the United States a shandy is usually made with ginger ale instead).
In Australia and New Zealand term "lemonade" is commonly used for colorless lemon or lemon-and-lime flavored soft drinks such as Sprite or 7up. Cloudy lemon soft drinks (like traditional American lemonades) are usually referred to as "lemon squashes" and often contain small amount of real lemon juice (i.e. Solo or Lift). A drink called Lemon Barley Cordial is probably the closest Australian equivalent to traditional American lemonade.
In Germany most sweet carbonated drinks, especially lemon-flavored beverages, can be referred to as "Limonade" or "Limo". These beverages are sometimes mixed with beer making a Radler (southern Germany)/an Alsterwasser (northern Germany), which is similar to a British shandy. A drink named "Limoschoppen" is made by mixing this lemonade with white wine.
In France lemonade is also a carbonated drink named "lemonade" in French manner. The drink that is called "lemonade" in America is often referred as Citron Pressé there. If you order one in a French café, you will probably get a shaker, fresh squeezed lemon juice, some ice cubes, sugar and water so you can prepare the drink to your taste.