For example, james roberts Smith was written as James R Smith, or simply omitted as james smith. In other English-speaking countries, people usually have more than one name, although their first name is more familiar. In other countries, the word "middle name" only refers to those names at the bottom of the position, but they are not surnames (for example, a person can use his mother's maiden name as a middle name).
In the United States, you can replace a middle name with its initials or religious initials, even if the name is not printed on the birth certificate. This method is sometimes used to replace middle names in identity documents, passports, driver's licenses, social security cards, university diplomas and official documents.
Examples of this form include George W. Bush and John D. Rockefeller. When a person doesn't have a middle name, sometimes the abbreviation "NMN" (no middle name) or "NMI" (no middle name initials) is used to fill in the place where the middle name or its initials are needed in the official document. The same is true for those who use their first names as their middle names.
Extended information for English-speaking countries:
Parents choose their children's first and middle names at the same time, and those frequently used names are often used as middle names. Due to traditional factors or to show respect, the first names given by relatives or other parents are often used as children's middle names. Other uses of middle names include giving children names that are inconvenient as names. For example, this name will become a social burden for children.
Sometimes surnames are also used as middle names to show respect for relatives. Especially in South America, it is common to use the mother's maiden name as the middle name. A child's middle name is sometimes the first name or middle name of one parent. In America, it is common to give a baby boy the same name as his father. At this time, the middle name will be used to distinguish.
A woman named Mary is often called by her middle name (or Mary) because the name Mary is used by many people. In the southern United States, close people are sometimes called "first name+middle name", such as "Mary Anne" or "John Michael".
Middle names are generally not used in daily life. However, some people with more familiar middle names may abbreviate their first names into initials. (such as Scott Fitzgerald and Somerset Mao Mu). Some people don't use names at all (such as paul mccartney, whose name is James).
In a few cases, a person's middle name may only contain one letter, which has no meaning. (For example, President Harry S. Truman of the United States) This custom is more common among Amish people, who usually use the initials of the mother's maiden name as their children's only middle name. So Sarah Miller's children will use their middle name [M]. The custom of abbreviating middle names into initials is rare in Britain.
References:
Baidu Encyclopedia-Middle Name