Can be created in each directory inside of a CVS working copy.
Contains regular expressions that match file or directory names.
CVS ignores files matching those expressions when performing commands such as cvs update.
Result is that you do not see the "?" before files not in repository.
Example:
*.swp *.log *.aux html
If there are some that you always want to ignore, you can create cvsignore (without the leading '.') in the CVSROOT part of the repository.