Final answer:
The part of the file name after the dot is the file extension, which indicates the file's format and helps the operating system decide which program should open the file.
Step-by-step explanation:
A file extension is a suffix at the end of a computer file. It comes after the dot in the file name and typically consists of three or four characters. This part of the file name identifies the file format or type and helps the operating system determine which program to use to open the file. For example, a file named 'document.docx' has a file extension of '.docx', which indicates it is a Microsoft Word document.
Similarly, 'picture.jpeg' has a '.jpeg' extension, suggesting it is an image file. Different file extensions represent different types of data and the software required to access them, such as '.pdf' for PDF readers, '.mp4' for video players, and '.html' for web browsers. It's important for users to be aware of file extensions to ensure proper usage and to maintain security, as some file extensions may represent executable files that can potentially carry risks if sourced from an unknown or untrusted origin.