Septic safe on toilet paper means that the septic safe toilet paper is designed and made to dissolve really fast or rapidly.
In a septic system or septic tank it's important that toilet paper dissolves pretty fast and breaks down in the septic tank so that the septic tank does not clog up or fill up to fast.
You still need to have your septic tank pumped out every 5 to 10 years depending on how often you use your septic tank and how fast it fills up.
You can use septic tank RidX as well to help dissolve solids and other stuff in the septic tank.
All toilet paper that is made today is usually septic tank safe and will dissolve just fine in the septic tank.
If you have a septic tank it's best to not use any thicker toilet paper unless it says septic safe.
Also do not flush wipes or other things such as cigarette butts etc into the toilet with a septic tank because it can cause the septic tank to clog up.