Assigned male at birth (AMAB) is used to indicate that a person was labeled male when they were born. Often, it refers to people whose bodies have male sex characteristics (such as a penis and tesicles), but it can also refer to people who are intersex and labeled male.
This term was developed in response to the idea that trans individuals "really" are a gender other than the one they are or were born another gender. Male assigned at birth (along with female assigned at birth) indicates that the individual in question was assigned a gender by an outside force when they were born rather than being that gender to begin with.
