Caritas is a Latin word meaning "love."

As used in scripture, it simply means "love", as in, Deus caritas est, "God is love."  1 John 4:8.  

In some versions of scripture, the word is translated into English as "charity" or sometimes simply as "God's love."

St. Thomas Aquinas understood it to mean "the friendship of man for God," the most excellent of virtues, in accord with 1 Cor 13:13 ("..but the greatest of these is love").  

This is why several organizations have Caritas within their name, such as CARITAS for Children, a global Catholic Apostolate specializing in Child Sponsorship.

As for the logo, that shape embracing the purple heart is not only intended to evoke a stylized letter "C," but also the image of a chalice, the sort intended to hold the blood of Christ.

The blood sacrificed for all through Love... 

With regard to the purple heart, purple has long symbolized royalty and other high privilege designating Christ Jesus, the fulfillment of God's eternal love, the Davidic King, Messiah and Savior of the World. 

And as God is Love, Catholics hold the belief that 

...if I should have all faith, so that I could move mountains, and have not "caritas", I am nothing.  1 Corinthians 13:2