A girl is any female human from birth through childhood and adolescence to attainment of adulthood when she becomes a woman. The term may also be used to mean a young woman. The word is also often used as a synonym for daughter.
Etymology
The English word girl first appeared during the Middle Ages between 1250 and 1300 CE and came from the Anglo-Saxon words gerle (also spelled girle or gurle).The Anglo-Saxon word gerela meaning dress or clothing item also seems to have been used as a metonym in some sense.
Girl has meant any young unmarried woman since about 1530. Its first noted meaning for sweetheart is 1648. The earliest known appearance of girl-friend is in 1892 and girl next door, meant as a teenaged female or young woman with a kind of wholesome appeal, dates only to 1961
Girls develop female characteristics by inheriting two X chromosomes (XX), one from each parent. About one in a thousand girls have a 47,XXX karyotype, and one in 2500 have a 45,X one. Girls typically have a female reproductive system. Some intersex children with ambiguous genitals, some transgender children, originally assigned male at birth, may also be classified or self-identify as girls.
Girls' bodies undergo gradual changes during puberty. Puberty is the process of physical changes by which a child's body matures into an adult body capable of sexual reproduction to enable fertilisation. It is initiated by hormonal signals from the brain to the gonads. In response to the signals, the gonads produce hormones that stimulate libido and the growth, function, and transformation of the brain, bones, muscle, blood, skin, hair, breasts, and sexual organs. Physical growth—height and weight—accelerates in the first half of puberty and is completed when the child has developed an adult body. Until the maturation of their reproductive capabilities, the pre-pubertal, physical differences between boys and girls are the genitalia, the penis and the vagina. Puberty is a process that usually takes place between the ages 10–16, but these ages differ from girl to girl. The major landmark of girls' puberty is menarche, the onset of menstruation, which occurs on average between ages 12–13.
source :http://en.wikipedia.org/wiki/Girl
the girl on image
