file name extension
1. A suffix that is preceded by a decimal (“. “) and that is appended to a computer file name.
Note: Common filename extensions with their meanings are: . wpd = a type of word-processing document . doc = a type of word-processing document. exe = executable code or a self-extracting archive file. . gif = a graphical interchange format (graphics file). txt = a text file.
2. Proprietary HTML tags that are recognized by a single Web browser or by those Web browsers developed by a single company.