Foreign institutional investors (FIIs) refer to institutional investors that are based in a different country but invest in financial assets in another country. These investors include hedge funds, mutual funds, pension funds, insurance companies, and other similar entities. The portfolio investment made by these foreign institutional investors is known as FII investment.

Here is a detailed explanation of why the correct answer is option 'B' - FII:

FII - Foreign Institutional Investors:
Foreign institutional investors are entities that invest in the financial markets of a country other than their own. They purchase stocks, bonds, and other financial instruments of companies listed on the country's stock exchange. FIIs are regulated by the securities and exchange board of India (SEBI) in India and similar regulatory bodies in other countries.

Explanation of Other Options:
a) FDI - Foreign Direct Investment: Foreign direct investment refers to the investment made by a foreign entity in the business operations of a company in another country. FDI involves the acquisition of a substantial ownership stake in the company and is typically associated with long-term investments that have a direct impact on the company's operations and management.

c) Balance of Payment: The balance of payments is a record of all economic transactions between the residents of a country and the rest of the world during a specific period. It includes both current account transactions (such as trade in goods and services) and capital account transactions (such as investments and loans).

d) SDR - Special Drawing Rights: Special Drawing Rights are a form of international reserve assets created by the International Monetary Fund (IMF). SDRs are used as a unit of account and a means of exchange between member countries. They are allocated to member countries in proportion to their IMF quotas and can be used to settle international transactions.

Conclusion:
In conclusion, the portfolio investment made by foreign institutional investors is called FII investment. It is important to understand the distinction between FII investment and other types of foreign investments such as FDI, balance of payment, and SDR. FII investment plays a significant role in the global financial markets and can have a significant impact on the economies of the countries in which they invest.