Answer:
Nowadays, a joint stock company is simply a corporation whose stockholders can buy or sell the company's stocks. But 4 centuries ago, joint stock companies were very different.
Joint stock companies were used by the British Empire to set colonies around the world, e.g. the Virginia Company was chartered rights to establish and exploit colonies in British territories, which are now the US.
A joint stock company was named that way because stocks of the company were sold to rich people in England that were willing to risk money in the colonies. E.g. Jameston was founded and basically owned by the Virginia Company. Joint stock companies were vital for the colonization processes of the British Empire.
The King of England could also establish chartered companies which basically had a monopoly over the trade of certain areas, e.g. the East India Company was probably one of the most famous of them and the most powerful and wealthy.
Some chartered companies were even responsible for paying the salaries and expenses of the British government officials in foreign countries. The East India Company basically ruled over all India and had its own private army.
