Manual:$wgUploadDirectory

Details
The file system path of the folder where uploaded files will be stored.

This location needs to be writable by the web server.

See upload>Special:MyLanguage/Manual:Configuring file uploads#Check directory security|Manual:Configuring file uploads#Check directory security.

By default, uploaded files are actually stored in subfolders of $wgUploadDirectory.

See upload>Special:MyLanguage/Manual:Configuring file uploads#Upload directory|Manual:Configuring file uploads#Upload directory for information, and how to disable this behavior.