1) The term "bull market" refers to a period of rising stock prices, while a "bear market" refers to a period of falling stock prices.

2) The word "piano" contains three vowels: I, A, and O.

3) The process of nuclear fusion powers the sun and other stars, fusing hydrogen atoms together to form helium and releasing vast amounts of energy in the process.

4) In Greek mythology, the Trojan War is a legendary conflict between the city of Troy and the Greeks, sparked by the abduction of Helen of Troy. It is immortalized in Homer's epic poems, the Iliad and the Odyssey, and features famous heroes like Achilles, Hector, and Odysseus.