Gratitude, thankfulness, or gratefulness is the proper, fitting or called-for response to benefits or beneficence from a benefactor. The experience of gratitude has historically been a focus of several world religions. It has also been a topic of interest to ancient, medieval and modern philosophers, and continues to engage contemporary western philosophers today. The systematic study of gratitude within psychology only began around the year 2000, possibly because psychology has traditionally been focused more on understanding distress rather than understanding positive emotions. The study of gratitude within psychology has focused on the understanding of the short term experience of the emotion of gratitude (state gratitude), individual differences in how frequently people feel gratitude (trait gratitude), and the relationship between these two aspects.
–Wikipedia