Blood Sugar is the Sugar that is transported through our bloodstream to different cells in our body so that these cells generate energy from it to keep us alive. Glucose is a simple form of Sugar that is transported by our blood and it is the only form of sugar that can be utilized by our body for generation of energy.
So, blood sugar always means blood glucose.
When we eat food, it gets digested in our body and gets converted into glucose. This glucose goes straight from our digestive system into our bloodstream.