A kurta is typically a male form of a kurti. Although people use the term interchangeably, the word kurta is more universal and well known for the attire being referred to. Most people do not know or understand the difference in both terms or the relations to gender.
Although in design both kurta and kurti are the same, sometimes a kurta is referred to as the casual version of the kurti. It can also be referred to sometimes as the longer version of the two.