The flag of Lebanon (Arabic: علم لبنان) is formed of two horizontal red stripes enveloping a horizontal white stripe. The white stripe is to be two times a red one (ratio 1:2:1)—a Spanish fess. The green cedar in the middle touches each of the red stripes and its width is one third of the width of the flag.
It was designed to be a neutral flag, not allied to any one of Lebanon's religious groups. The red stripes symbolize the pure blood shed in the aim of liberation. The white stripe symbolizes peace, and the white snow covering Lebanon's mountains. The green cedar, (Species: Cedrus libani or Lebanon Cedar) symbolizes immortality and steadiness.
This cedar is referenced many times in the Bible: "The righteous flourish like the palm tree, and grow like a cedar in Lebanon" (Psalms 92:12). There is also some reference in W. Smith's 1980 book on the colors: "The red and white colors are those associated, respectively, with the Qaysites and Yemenites, opposing clans that divided Lebanese society between 634 and 1711 AD". However, that explanation is poorly known (not to mention quite unheard of) in the Lebanese tradition.
It is a common mistake to draw the branches of the cedar and the tree trunk in brown or black which could be seen as unconstitutional. The cedar should be fully green regarding the provisions in the Constitution.