An infant (from the Latin word infans, meaning "unable to speak" or "speechless") is the very young offspring of a human or other mammal. When applied to humans, the term is usually considered synonymous with baby, but the latter is commonly applied to the young of any animal. When a human child learns to walk, the term toddler may be used instead.

The term infant is typically applied to young children between the ages of 1 month and 12 months; however, definitions vary between birth and 3 years of age. A newborn is an infant who is only hours, days, or up to a few weeks old. In medical contexts, newborn or neonate (from Latin, neonatus, newborn) refers to an infant in the first 28 days after birth; the term applies to premature infants, postmature infants, and full term infants. Before birth, the term fetus is used.

Infant is also a legal term referring to any child under the age of legal adulthood.

A newborn's shoulders and hips are wide, the abdomen protrudes slightly, and the arms and legs are relatively long with respect to the rest of their body. In first world nations, the average birth weight of a full-term newborn is approximately 3.2 kg.(7 ½ lbs), and is typically in the range of 2.7–4.6 kg (5.5–10 pounds). The average total body length is 35.6–50.8 cm (14–20 inches), although premature newborns may be much smaller. The Apgar score is a measure of a newborn's transition from the uterus during the first minutes after birth.

A male sibling is called a brother; and a female sibling is called a sister. In most societies throughout the world, siblings usually grow up together development of strong emotional bonds such as love, hostility or thoughtfulness. The emotional bond between siblings is often complicated and is influenced by factors such as parental treatment, birth order, personality, and personal experiences outside the family.

Sibling is a modern revival of the Old English word sibling, meaning "relative, kinsman", a derivative of sibb "kinship, relationship", from Proto-Germanic *sibjō "race", from Proto-Indo-European *sebh-, *s(w)ebh- "tribe, one's own people". The term, along with its shortened form sib, may have been in use dialectally throughout the Middle English and Early Modern English periods, but was officially recognized c. 1903 when it came into common use in anthropology as a translation of the German genetics term Geschwister ("a brother or sister"). The word is further related to the second part of the word gossip, which derives from Old English gōdsibb, meaning "a sponsor, close relation".

War is an organized, armed, and often a prolonged conflict that is carried on between states, nations, or other parties typified by extreme aggression, social disruption, and usually high mortality. War should be understood as an actual, intentional and widespread armed conflict between political communities, and therefore is defined as a form of political violence. The set of techniques used by a group to carry out war is known as warfare. An absence of war (and other violence) is usually called peace.

In 2003, Nobel Laureate Richard E. Smalley identified war as the sixth (of ten) biggest problems facing the society of mankind for the next fifty years. In the 1832 treatise On War, Prussian military general and theoretician Carl von Clausewitz defined war as follows: "War is thus an act of force to compel our enemy to do our will."

While some scholars see warfare as an inescapable and integral aspect of human culture, others argue that it is only inevitable under certain socio-cultural or ecological circumstances. Some scholars argue that the practice of war is not linked to any single type of political organization or society. Rather, as discussed by John Keegan in his History of Warfare, war is a universal phenomenon whose form and scope is defined by the society that wages it. Another argument suggests that since there are human societies in which warfare does not exist, humans may not be naturally disposed for warfare, which emerges under particular circumstances. The ever changing technologies and potentials of war extend along a historical continuum. At the one end lies the endemic warfare of the Paleolithic^{[citation needed]} with its stones and clubs, and the naturally limited loss of life associated with the use of such weapons. Found at the other end of this continuum is nuclear warfare, along with the recently developed possible outcome of its use, namely the potential risk of the complete extinction of the human species.