In music notation, a tie is a curved line which connects two notes of the same pitch on different sides of a bar-line, joining them into a single note. For instance, two quarter notes joined by a tie would be equivalent to a single half note. A tie resembles a parenthesis tipped on its side.
A tie looks something like this on the staff:
_---_
/\ / \
---| /--------------------------|------------------|-------
|/ * | * |
---/--------------------*---|---|--|----*----------|-------
/| 4 * | | | | | * |
-/-|/\--------*---|----|----|---|--|---|---|----*--|-------
| | | 4 | | | | | | | | | |
|--|--|------|----|----|--------|------|---|---|---|-------
\ | | | | | | | |
--\|_/-------|------------------|--------------|---|-------
|
\|