Input types is a list of file content types that the print filter can process. The LP print service does limit the number of input types, but most filters can accept only one input type. Several file types can be similar enough, such that the filter can deal with them. You can use whatever names you prefer, with a maximum of 14 alphanumeric characters and dashes. Do not use underscores as part of the input type name.
The LP print service uses these names to match a filter to a file type, so follow a consistent naming convention. For example, if more than one filter can accept the same input type, use the same name for that input type when you specify it for each filter. Inform your users of these names so that they know how to identify the file type when submitting a file for printing.