The Hanuman Chalisa is a Hindu devotional hymn (stotra) addressed to Lord Hanuman. It is traditionally believed to have been authored by 16th century poet Tulsidas in the Awadhi language.
The word Chalisa is derived from Chalis, which means the number forty in Hindi, as the Hanuman Chalisa has 40 verses (excluding the couplets at the beginning and at the end).
It is recited to get energy and concentration. Hanuman is the source of immense energy and focus.