Hidden Files / Directories in Ubuntu are those directories whose contents are usually not displayed by default. Name of these kind of files / directories starts with . (dot). They are generally used for saving user choices or keeping away the state of a service and are usually made without even questioning by utilizing several services.
Hiding files and directories in Linux is considered to be pretty simple. All you require to add . (dot) at the beginning of the name of the file/directory as shown below.
$mv filename .filename
To view/list hidden files you need to add -a in ls command.
Hide a file/ directory using GUI
Also you have another alternative i.e with the help of your keyboard. Click on the file, press the F2 key and add a dot (.) at the beginning of the name of the file. To view hidden files and directories press Ctrl+H. The same keys will also re-hide exposed files.