Some people only feel sexual attraction toward those with whom they have developed a strong personal bond. If this is the case, the person is known as being demisexual.
According to the Demisexuality Resource Center, a person who is demisexual will feel sexual attraction and desire to engage in sexual activities far more rarely than the general population.
For example, most people can feel sexually attracted to random people whom they meet in public or at work or school. In some cases, this is based purely on physical attraction and comes from simply seeing the person.
In contrast, a demisexual will only feel sexual attraction toward a person once they have had the chance to develop a strong emotional bond with them. If they feel a sexual attraction toward a person, they may choose to engage in sexual activity with them, but the urge is often weaker. In some cases, it may never develop, despite the emotional connection.