In music what is a tie?

In music, a "tie" is when you connect two notes that happen one after another and are the same pitch. They are connected into one continuous note. The marking used on sheet music is a curved, gentle arch-like indication connecting the two (or more) notes wanting to be "tied". This curved line is basically the same as a slur/legato/connection marking but between two (or more) notes of the same pitch.