Iron Saturation is a ratio calculated from serum iron and transferrin. Serum iron is how much iron is floating around free, unbound, in your blood. Transferrin is made in the liver, and is a tool the body uses to encapsulate unbound iron for later use. Transferrin is useful for keeping iron-loving bacteria from using up all the iron you eat.

Generally, you have to look at all three measurements together to get a correct picture of your iron status. One measurement taken alone doesn't tell you anything.

This chart explains it pretty well:

https://en.wikipedia.org/wiki/Total_iron-binding_capacity#Interpretation

Your situation is the one in the bottom row of that chart. When serum iron levels are normal, and transferrin is high, the iron saturation can be on the low end. It doesn't indicate that anything is wrong. It just means your liver has created a lot of transferrin to reserve all the iron you eat, just in case it needs it later. Pregnancy and birth control are two things that raise transferrin levels and therefore lower the saturation level.

HOWEVER, as you can see in the chart, serum iron levels are highly variable. Using bloodwork alone to diagnose anemia is why generally people don't get diagnosed until their anemia is severe. If you have symptoms like fatigue, heart palpitations, muscle soreness or weakness without having exercised, feeling out of breath easily, then you should take further steps to ensure you're not heading toward anemia.

If you do take iron, you should also take B12, vitamin A and K and copper. Or, eat beef liver which has all of these. If you eat a 4oz piece of beef liver and feel different the next day, that's an indication you are deficient in one or more of these nutrients.