A Bhajan is a type of Hindu devotional song, often simple, lyrical and expressing love for the Divine. The music is sometimes based on classical ragas and talas. Traditions of bhajan such as Nirguni, Gorakhanathi, Vallabhapanthi, Ashtachhap, Madhura-bhakti and the traditional South Indian form Sampradya Bhajan each have their own repertoire and methods of singing.
Anecdotes and episodes from the lives of Gods, the teachings of saints and descriptions of gods' glories have been the subject of bhajans. The Dhrupad style, Sufi qawwali[1] and the kirtan or song in the Haridas tradition are related to bhajan. Nanak, Kabir, Mirabai, Narottama Dasa, Surdas and Tulsidas are notable composers.
Kirtan (Sanskrit: "to repeat")[1] is call-and-response chanting performed in India's devotional traditions.[2]. When this chanting is done as a private meditation it is called japa, but when performed congregationally with instruments and often dancing it is called kirtan or sankirtan (from san, meaning "complete" +kirtan).[3] A person performing kirtan is known as a kirtankar.
In the Bhagavad-gita (9.13)[4] Krishna states that great souls are always engaged in glorifying him with kirtan. The practice was popularized in the Hindu devotional revival of the 15th century CE.
Kirtan practice involves chanting hymns or mantras to the accompaniment of instruments such as the harmonium, the two-headed mrdanga or pakawaj drum and karatal hand cymbals. It is a major tenet of Vaisnava devotionalism, Sikhism, the Sant traditions, and some forms of Buddhism, as well as other sects.
Additional Resources
http://bhajans.org/dynamic/