Refers to using something for one's own private purposes, not for business or public use.
This software is for personal use only.
You must not use company equipment for personal purposes.
私用 also means 'private use' but often implies using something for personal errands or private matters, sometimes with a nuance of misusing company time or resources. 個人使用 is more neutral and simply states the purpose is personal, not commercial or official.
Compound of 個人 (individual, personal) and 使用 (use, usage).