Yosemite 10.10.5 disk full

What is “Other” storage on a Mac, and how can I clean it out?

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The final word from Apple on Managing the " Other " Category

Other: Contains files that don’t fall into the categories listed here. This category primarily includes files and data used by the system, such as log files, caches, VM files, and other runtime system resources. Also included are temporary files, fonts, app support files, and plug-ins. You can't manage the contents of this category. The contents are managed by macOS, and the category varies in size depending on the current state of your Mac.

FYI, you should never let a drive fill up completely as it can lead to problems such as a corrupt file system and possibly corrupt files if using HFS+. With APFS (macOS 10.13+) running out of storage space may make it impossible to delete any files. A macOS boot drive should always have at least 20GB of free storage space for the normal operation of macOS.

Not to be insulting, but have you remembered to empty the Trash?

You may want to disable any file syncing services as they may be repopulating the drive as you clear up more space.

Also close all open apps which may release some files especially temp & cache files.

Make sure you have a good backup of all your data before you attempt to reboot the computer. If the drive is completely full, then rebooting the computer may not work and you may have trouble accessing those files if you don't have another macOS boot drive. If you have a good backup and have tried everything possible to free up storage space, then try rebooting into Safe Mode which should delete some temp & cache files during boot which will give you the best chance of booting the Mac again until you can free up storage space.