Hanuman chalisa is very popular among a lot of modern hindus and is generally recited on Tuesdays (considered a holy day for devotees of Lord Hanuman).It is a poem and chalisa here means forty (chalis in Hindi) verses. The structure of the poem is extremely simple and rhythmic, thus making it all the more popular. The poem praises Lord Hanuman’s strength and kindness and recounts the Lord’s great deeds.
Hanuman occupies a unique place of reverence in the Hindu pantheon for his exemplary devotion to his King "Ram"and his unbelievable acts to serve the cause of his Master. Hanumanji was born to Anjana, so also called anjana putra. It is said that the childless King Dasaratha performed “Putrakama Yagna” to have children. After the “Yagna” was over, he got divine “payasam” for his wives. On consuming the “payasam”, his wives later gave birth to Rama, Lakshmana, Bharat and Shatrughna. A kite took a portion of the “payasam” and flew away. It dropped the “payasam” at the place where Anjana was praying to Lord Shiva for blessing her with a son. In the meantime, Pavan, the god of wind, put the falling “payasam” on Anjana’s palm. On having the “payesam”, Anjana got Hanuman as her son. Because of Pavan’s instrumental role in his birth, Hanuman is also called “Pavan Putra”
This and numerous other names of hanuman are a part of hanuman chalisa.