The best-known image of the Romanian flag is one with a hole in the middle. During the revolution of December 1989, protesters cut the communist emblem out of the yellow stripe and carried what was left. The emblem was formally abolished on December 27, and the flag that remained is the one Romania flies today.
Blue, yellow, red
Three vertical stripes of equal width run from the hoist: dark blue, then yellow, then red. Blue is read as liberty, yellow as justice, red as fraternity. The format came from the French tricolor, which shaped flag design across much of 19th century Europe.
The colors were in use well before the country was. Wallachian revolutionaries carried them in the 1830s against Ottoman rule, and during the revolutions of 1848 the tricolor became the emblem of the national movement in both Wallachia and Moldavia, the two regions that later formed Romania. The constitution of 1866 named blue, yellow, and red as the colors of the United Principalities, and the following year the Assembly of Deputies settled the arrangement: vertical stripes, blue at the hoist, exactly as in 1848. It survived every regime that came after, though not untouched. Each one put its own arms or seal in the middle stripe, and that is the part that came out in 1989.
Where it flies
The flag flies at government buildings, military establishments, and schools, and it is central to Great Union Day on December 1 and Independence Day on May 9. Protocol and production standards are set in law, which keeps the shade and proportions consistent. Romanians carry it to protests as readily as to football matches.
Romania and Chad
Chad's flag has the same three colors in the same order, and telling the two apart is genuinely difficult. The resemblance is coincidental: Romania's tricolor dates to the 1800s, Chad's to 1959, and neither country has been willing to change.
Moldova uses the same colors with a coat of arms in the middle, which at least makes it distinguishable across a room.
References
Romanian Government Official Publications on National Symbols