It is a condition in which the penis doesn’t grow during puberty and remains in a semi-infant stage. Men with micropenis do have erections and reproductive capabilities such as sperm production and ejaculation just like other men with normal penis.
There is also a medical condition called AIS (Androgen Insensitivity Syndrome) which can lead to micropenis. For men with AIS, they will only have stunted penis growth, but they will not have any female hormonal characteristics such as development of breasts, reduced body hair, soft skin etc., Men with AIS will have same male characteristics similar to other men with a normal penis.