How to make recoll list only folder or directory names instead of files? Or how to filter category to only search for directory names not directory contents (files)? Many times, I can only remember the folder's name not the file names. Thank you for your help.
Don't use recoll for that. recoll is for searching based on file content. It builds and index of your files so that you can then run full text searches on the content of your computer.
By definition, this doesn't apply to directories at all. (You can search based on files names with recoll too if you go to: Tools -> Advanced Search -> File name matching. Don't know how to restrict that to directories, though )
What you want to do is use a simpler method, such as find (CLI), locate, (CLI) or the searching utility that's integrated into nautilus (pops up when you press CTRL+F). These do not look inside your files/directiories but only search for files/directiories based on their names.
I don't think you can specify 'directories only' with locate and nautilus's search, but you can certainly do that with find (though it will probably be somewhat slower, as find doesn't build a database for faster searches).
Try (in the command line) find $STARTING_POINT -name $QUOTED_WILDCARD_EXPRESSION_TO_SEARCH_FOR -type d (type d means type=directory)
OR use nautilus search and have the results listed by type (so that you can select directories only).
You can start looking for something better if none of these method is fast enough for you (if you want to run searches on a very large set of directories).
While I agree with the previous answer (recoll not the best tool for file searches), and for the record, you can filter answers for being directories only by using the query language with a mime specification of application/x-fsdirectory. For example searching for a directory with "bin" in the name would be:
This would return results such as bin or cgi-bin