Yes, brown hair is the second most common natural hair color. It comes in second behind black hair which is the most common hair color. Brown hair has many different shades and levels of color, so it makes sense that it would be the second most common color.
It can range anywhere from a very, very dark almost black color of brown to a very light, almost dirty blonde color and can even have blonde highlights. The color of your hair also plays a role in the thickness of the hair. People with blonde hair tend to have much thinner hair strands while people with red hair have much thicker strands.