It is quite common for someone to be known by a nickname. Charles Darwin’s brother, Erasmus Alvery Darwin, was allegedly known as “Eras”. The above example shows how the nickname can be entered. Entering a name here will then show it as a nickname on charts and in reports for example:
Usually, in reports, people are referred to by their full given name. However, if the “Prefer nickname” check box is set, then the full given name is only used in titles, and in normal narrative text, the nickname is used.
Although there are no hard rules, a nickname is usually something other than one of the formal given names, or possibly a shortened variant of one of them. Someone called John, might have a nickname of Jack for example, or Elizabeth, might have a nickname of Betty.