A wedding officiant is a person who is allowed by the government to perform weddings. This person may be a civil servant, or they may hold a religious position (for example, a priest or a rabbi). In some countries, certain religious officials are automatically allowed to perform weddings. In other countries, they must first ask permission from the government.
Wedding officiants who work for the government must often follow special rules, that others do not have to follow. For example, the government might not allow them to refuse to perform a wedding, if the people who want to get married are allowed to by the law.
Some countries allow anyone, not just civil servants or religious officials, to become wedding officiants temporarily. A temporary wedding officiant is usually allowed to carry out only one specific wedding that they asked permission for. If they want to perform another one, they have to ask the government for permission again.