Hanuman Chalisa is a devotional song(stotra) in praise of Lord Hanuman. It was composed by Goswami Tulsidas(best known for authoring the epic Ramcharitmanas) in Awadhi language(a language similar to Sanskrit and Hindi).
Chalisa means 40 verses and is derived from the Sanskrit word Chalis which means 40. Hanuman Chalisa is a chant of 40 verses in the glory of Lord Hanuman.
Tulsidas’ Hanuman Chalisa highlights Lord Hanuman’s power, energy, selfishness and his ultimate devotion to Lord Rama. It describes the paramount role that he played in the victory of Lord Rama over the demon king Ravana, the finding of Mother Sita and the procurement of the Sanjeevani herb for the recovery of Lakshmana. Hanuman Chalisa inspires spiritual aspirants to completely devote themselves to the supreme, Lord Rama so that they can get rid of all the pain and misery in their lives.
By reciting the Hanuman Chalisa, a devotee reminds himself of the wisdom, strength and courage of Hanuman. One who recites Hanuman Chalisa gets peace of heart and mind. Tulsidas states in the Chalisa that one who chants the Chalisa one hundred times becomes free from the bondage of life and death and enjoys the highest bliss at last.