In a computer language, “reserved words” are all those words that have a strictly predefined meaning—they are reserved for special use and cannot be used for any other purpose. For example, the words Start, End, Read, and Write in flowcharts have a predefined meaning. They are used to represent the beginning, the end, the data input, and the results output, respectively.
Reserved words exist in all high-level computer languages as well. In PHP, C++, C#, Java, Visual Basic, and Python there are many reserved words such as if, while, and for. Their meanings are predefined, so these words cannot be used for any other purposes.
Notice: Reserved words in a computer language are often called keywords.