A sibling is a brother or a sister; that is, any person who shares at least one of the same parents. In most societies throughout the world, siblings usually grow up together and spend a good deal of their childhood with each other. This genetic and physical closeness may be marked by the development of strong emotional associations such as love or enmity. The sibling bond is often complicated and is influenced by factors such as parental treatment, birth order, personality, and people and experiences outside the family. 
Types of siblings
A full sibling, is a sibling that shares both biological or adoptive parents.
A half sibling (half brother or half sister) is a sibling with one shared biological or adoptive parent. A half sibling that shares the same mother (but different fathers) is known as a uterine sibling, whereas one that shares the same father is known as an agnate sibling. In law, the term consanguine is used in place of agnate. Half siblings can have a wide variety of interpersonal relationships, from a bond as close as any full siblings, to total strangers.
At law (and especially inheritance law) half siblings were often accorded unequal treatment. Old English common law at one time incorporated inequalities into the laws of intestate succession, with half siblings taking only half as much property of their intestate siblings' estates as other siblings of full-blood. Unequal treatment of this type has been wholly abolished in England and throughout the United States.
A stepsibling (stepbrother or stepsister) is a sibling with whom a person bears no biologic or equivalent adoptive relation, and is related by the marriage or relationship of one parent of the person to one parent of the sibling.
Milk brothers or sisters are children breastfed by a woman other than their biological mother, a practice known as wetnursing and once widespread in the developed world, as it still is in parts of the developing world.
In Islam those who are fed in this way become siblings to the biological children of their wetnurse, provided that they are less than two years old. Islamic law (shariah) codifies the relationship between these people, and certain specified relatives, as rada; once they are adult, they are mahram, meaning that they are not allowed to marry each other, and the rules of modesty known as hijab are relaxed, as with other family members.
"Irish twins" and "Vatican twins" are slang terms for siblings who are not actually twins, but rather, were born fewer than 12 months apart —possibly in the same calendar year and/or school year. It refers to the perception that Irish Catholic families have many children, often with little time between births. It is sometimes considered derogatory. Similarly, "Irish triplets" refers to three siblings born within a three year time period.
A Godsibling (Godbrother or Godsister) is determined when one child is a Godchild of another child's parents. For example, if a child has a Godparent, and that Godparent has a child of his/her own, the child of the Godparent and the Godchild are Godsiblings. Godsiblings can either be related or non-related to each other.
Foster Siblings are children who are raised in the same Foster Home, or are also Foster Children of the person's Parents, or Foster Parents' biological children.
Economic interdependence and social fraternity will ultimately conduce to brotherhood. Man is naturally a dreamer, but science is sobering him so that religion can presently activate him with far less danger of precipitating fanatical reactions. Economic necessities tie man up with reality, and personal religious experience brings this same man face to face with the eternal realities of an ever-expanding and progressing cosmic citizenship.