Fertilizer is any substance used to add nutrients to the soil to promote soil fertility and increase plant growth. Notice how nothing in there mentions the actual soil health; that's because not all fertilizers are made the same and not all are healthy for the soil.
Soil health relies on a balance of macronutrients and micronutrients, as well as microbial health. It's vastly more complicated then simply adding nitrogen, phosphorus and potassium (NPK) to the ground and calling it a day.