Señorita is like Miss/Young lady as opposed to Madam/Lady (señora). Señorita is also sometimes used for unmarried women. There is an interesting discussion about this over on Spanishdict.com
Woman - mujer, lady- señorita, miss - señorita, girl- chica/muchacha/niña/chava/chama/piba, mrs- SEÑORA... "señora" aplies for a older or married woman, "señorita" aplies for young woman, single woman, etc... And The diminutive "ito" or "ita", it is used in all latin america and spain.. It is not just of some countries or regions... Un saludo!..