When you refinance to a lower rate, that reduces the size of your mortgage interest deduction, which affects your savings from refinancing. The Mortgage Refinance Calculator can take that into account, which is why it asks for your income tax rate.
Look up yo in Wiktionary, the free dictionary. Yo is an English slang interjection, commonly associated with American English. It was popularized after being used commonly by the Italian-American community in Philadelphia, Pennsylvania since the 1940s.
The Oxford English Dictionary dates yoo-hoo to 1924, as noted by the American Dialect Society, and compares it to yo-ho, originally a nautical phrase also sometimes used in yo-heave-ho. Their first documented use of yo-ho is from 1769 in William Falconer's An universal dictionary of the marine: Hola-ho, a cry which answers to yoe-hoe.