The Pali word metta is a multi-significant term meaning loving-kindness, friendliness, goodwill, benevolence, fellowship, amity, concord, inoffensiveness and non-violence. The Pali commentators define metta as the strong wish for the welfare and happiness of others (parahita-parasukha-kamana).
Essentially metta is an altruistic attitude of love and friendliness as distinguished from mere amiability based on self-interest. Through metta one refuses to be offensive and renounces bitterness, resentment and animosity of every kind, developing instead a mind of friendliness, accommodativeness and benevolence which seeks the well-being and happiness of others.
True metta is devoid of self-interest. It evokes within a warm-hearted feeling of fellowship, sympathy and love, which grows boundless with practice and overcomes all social, religious, racial, political and economic barriers. Metta is indeed a universal, unselfish and all-embracing love.
Source: “Metta: The Philosophy and Practice of Universal Love”, by Acharya Buddharakkhita. Access to Insight, 5 June 2010, http://www.accesstoinsight.org/lib/authors/buddharakkhita/wheel365.html . Retrieved on 5 June 2012.