When a man or woman having children shall remarry, the new partner can also be your children from a previous marriage. In this case, their children will be half brothers and sisters. Thus, the half-brother is the son stepmother or stepfather, it is not a biological relative. A half-brothers (and sisters) there is no common parents, while they live in the same household, i.e., they are "summarized" into one family.
This situation in social and legal sense is classified as nekrovnoe relationship. In this summary brothers and sisters can be blood relatives through their descendants. This is possible if the wife and husband with children from a previous marriage (stepbrothers/sisters), born children, who are half and half for older children. The descendants of those, and others will be in kinship.
Often the summary incorrectly referred to as siblings with a common father (consanguineous) or a common mother (uterine).
Named (or called) brother, in contrast to the consolidated, is not even a formal relative. He is not native by blood, but my own mental and emotional plane. This is usually a close friend, with whom lot lived, whom a lot in common and you can rely on. When people call each other brothers named, it speaks of deep friendship and trust between them.
In Russian folk tales called brother is the one who made a vow to be someone's brother, i.e. "called a brother", fraternized. The word "called" are synonyms - sister, paratenic that were more widely used in the past.
Also in ancient times there was the practice of the exchange of crosses between close friends. Such people are called cross or, again, named brothers. The relationship between them was called the crusade of brotherhood or fraternity, which suggested clear standards of conduct and voluntary commitments of mutual assistance. In a Russian Bylina "Dobrynya Fight with Ilya Muromets" describes the heroes Ilya Muromets and Dobrynya Nikitich, after which they first worthy opponents, become sworn brothers, Phillips brothers. Ilya Muromets, the eldest and won the match, becoming a big brother, and lover - less.
The second meaning of the word "called" - a non-native adopted son (or daughter), and for native children adopted alien child of his parents, he is called brother. This meaning is considered obsolete.