Hybrid are half-human, half-Visitor.
In the original V, Diana wanted to perform an experiment when human female would carry a hybrid child, half Human, half V. When Robin Maxwell to abort the child, the human doctors find it impossible, for that her biology had somewhat changed. When she gave birth to twins, one was a human-looking child but with a reptillian tongue, whilst the second was a V-looking. Although the reptillian looking child died because of how a bacteria formed in the child which would form the basis of the Red Dust. The human-looking one survived, and showed reptillian capabilities such as having venom, to shed skin, which according to Willie was too sooner than a normal V would.
In the remake of V, Ryan was told by scientists that it was impossible for a hybrid to ever happen, but apparently, Valerie was pregnant and was going to have a hybrid. During the pregnancy, Valerie was drained of phosphorous and needed a supplement for her to survive. The growth of the baby was accelerating far faster than that of an ordinary human baby. When Anna learned of the hyrbid, she called a meeting with the top surgeons of the 29 ships. Anna exclaimed that the existence of this baby puts the entire V species at risk, for that a hybrid can be born with human emotion: Love. And went on to say that the Fifth Column can breed an entire generation of hybrids to fight against the Visitors. Calling it a mongrel, a threat to their survival, ordered the surgeons to prematurely place the Live Aboard Programme into the next stage which was experimentation. Anna then ordered that the hyrbid parents be captured, but when V guards failed, she then ordered the deployment of a V soldier to apprehend the parents. Once the parents have been found, Joshua was ordered to dissect them to find out how this pregnancy came to be and how it could be stopped, and wanted the baby to be destroyed, for she found it an obstacle in their plans.
When Valerie was captured, she was already in labour, and so the V doctors onboard the mothership were helping Valerie give birth. When she gave birth, Anna was pleased the baby survived, but the mother however did not because Anna gave her a fatal injection which killed her. Ryan, in emotional dispair believed Anna killed her, but Anna lied and said "you said yourself I have use for her, why would I kill her?" and went on to say that the doctors did everything they could to keep her alive, and had Ryan come to them earlier they could've used the technology to save her life.
The baby in the remake is immediatly not seen, apart from a brief appearence of it's tail and making sounds which, although are gurgling, they don't sound like a human baby. The baby is reptillian for it had a tail, hinting that it's appearence is reptillian but have some human capabilities inside, such as human emotion.
In Red Rain, we now see the face of the hybrid and learn it's gender: female. It is being hold in a tank full of dark green liquid, and is undergoing tests to find out why this hybrid was born. Anna is not only using the child to find answers as to why it was born, but to use it against Ryan, since he is in the Fifth Column. Since Anna has his child she can use her against him, so Ryan would be forced to obey Anna, which therefore makes Ryan a spy, a window of opportunity for Anna to destroy the Fifth Column from within.
The V's plans are to actually to inter-breed with humans to create a next generation of V's. However there is a problem with this; the hybrids would feel human emotion and disobey their queen.