The phrase "system update" means making changes or improvements to the software or operating system on a computer or device to fix problems and add new features. Full definition
On pretty much any Android phone, when you check for operating system updates the phone contacts the manufacturers servers to see if there's new software available. (howtogeek.com)
You can check manually on the Fire by going to Settings > Device Options > System Updates > Check Now. (blog.the-ebook-reader.com)
We're getting ready for the next major system update for PS4, and can use some help from PS4 owners to test it out ahead of launch. (blog.us.playstation.com)