Tavuttaa means ”to hyphenate.”
Tavutus is ”hyphenation” or ”syllabification”
Tavuviiva is a hyphen used to divide words between two lines. (Literally, ”syllable line.”)
Väliviiva is a hyphen used in compounds with colliding vowels (e.g. linja-auto).
Also see yhdysviiva and yhdysmerkki which are terms describing the hyphenation of compounds.
Ajatusviiva means ”dash.” (Literally, ”idea line.”)
Viiva means ”line,” and it’s what you say when reading a number aloud that has a hyphen in it (for example, your henkilötunnus).
(For grammar junkies, a hyphen is used to connect two words to indicate that those words go together. A dash is a break in thought which distinguishes for the reader that there are two different thoughts being articulated.)