What is the Difference between Step-brother and Half-brother?
Half-brother is the son of your father and your step-mother or the son of your mother and step-father. So, you share one parent together which makes you related by blood.
On the contrary, you don’t have any blood relationship with your step-brother since he is the son of your step-father and his spouse or step-mother and her spouse. To be well-informed and avoid confusion, neither do your step-father and his spouse have a blood relationship with you nor do your step-mother and her spouse.
In short, your half-brother is related to you by blood, and your step-brother is NOT related to you by blood.