The four immeasurables, known also by the Sanskrit Brahma Viharas, are found throughout Buddhist traditions. They are summed up in this meditation/prayer:

May all sentient beings have happiness and its causes,
May all sentient beings be free of suffering and its causes,
May all sentient beings never be separated from bliss without suffering,
May all sentient beings be in equanimity, free of bias, attachment and anger.

The Buddha taught these to his son Rahula:

Rahula, practice loving kindness to overcome anger. Loving kindness has the capacity to bring happiness to others without demanding anything in return.

Practice compassion to overcome cruelty. Compassion has the capacity to remove the suffering of others without expecting anything in return.

Practice sympathetic joy to overcome hatred. Sympathetic joy arises when one rejoices over the happiness of others and wishes others well-being and success.

Practice non-attachment to overcome prejudice. Non-attachment is the way of looking at all things openly and equally. This is because that is. Myself and others are not separate. Do not reject one thing only to chase after another.

I call these the four immeasurables. Practice them and you will become a refreshing source of vitality and happiness for others.

From Thich Nhat Hahn's Old Path White Clouds"

Lovingkindness, or metta as it is known in Pali, is a universal, unselfish and all-embracing love that protects, supports and heals both oneself and others. Metta is one of the four immeasurables.