What does tis of thee mean?

The phrase "tis of thee" is a shortened version of the phrase "this is of thee". It is often used to refer to the United States of America, as in the line "this land is your land, this land is my land" from the song "This Land Is Your Land" by Woody Guthrie. The phrase "tis of thee" can also be used to refer to a specific person or thing, as in the line "I love the way you smile at me, 'tis of thee" from the song "The Way You Look Tonight" by Jerome Kern and Dorothy Fields.