All terms
Shareholder (Aktionär)
A person or institution that owns shares in a company.
As soon as you buy a share, you are a shareholder (German: Aktionär). You are a part-owner, but you are not liable for the company's debts: you cannot lose more than the money you put in.
Shareholders have rights. You may attend the annual general meeting, vote there, and receive a dividend if one is approved.
Example: with 20 ordinary shares of a DAX company you have 20 votes at its general meeting. That is little, but legally you are an owner just like a large fund.