MtM

The MtM flag.

MtM (Male-to-Male) is a term for transgender men who considers themselves transitioning from male to male, as they has always been male, just not in the way being male is traditionally defined as. They have always been male regardless of whatever genital, hormonal, or chromosomal arrangements they were born with, and whether they chooses to make changes to their body or not. It is an alterative to FtM as FtM implies that one was female, then transitioned to male. Female-to-male is a framing that’s easier to explain, but only because it's still rooted in the concept of binary sex distinctions and assuming gender based on sex, which a lot of trans people want to do away with entirely.