I changed it like this: \marginnote{A directory is a division of space in a file system used to organize files. A folder is the name given to a directory in a Graphical User Interface (\acronym{GUI}) environment.}
I changed it like this:
\marginnote{A directory is a division of space in a file system used to organize files. A folder is the name given to a directory in a Graphical User Interface (\acronym{GUI}) environment.}