What is the difference between "an utterance of our lips" and "speech"?
In the Viduy (confessions) that we say as part of the Yom Kippur prayers, there's a section where we list a whole bunch of sins, saying "Al chet..." (for the sin...) before each one. Two of the sections in the first third go like this:
על חטא שחטאנו לפניך בבלי דעת
ועל חטא שחטאנו לפניך בבטוי שפתים
For the sin we have sinned before You unwittingly,
and for the sin we have sinned before You by an utterance of our lips.
על חטא שחטאנו לפניך בדעת ובמרמה
ועל חטא שחטאנו לפניך בדיבור פה
For the sin we have sinned before You knowingly and deceitfully,
and for the sin we have sinned before You in speech.
(translations from the Koren Rohr Edition Yom Kippur Machzor, translated by Rabbi Lord Jonathan Sacks)
There are several other sins mentioned involved speech - eleven, according to Rabbi Sacks's commentary - but in the other cases, it's easier to understand what the differences are. Lashon hara is a familiar term for slander, and terms such as "impure speech" are differentiated enough to not cause confusion.
I'm struggling to understand what the different between "vituy s'fatayim" and "dibur peh" are. As far as I understand, the expressions are functionally the same. What is the difference between these two sins?
בבטוי שפתים By an utterance of our lips. Note how many of the sins enumerated here have to do with speech (eleven out of the forty-four). The sages took "evil speech" with utmost seriousness. They said it is as bad as the three cardinal sins — murder, forbidden sex, and idolatry — combined (Arakhin 15b). It kills three people: the one who says it, the one who listens to it, and the one about whom it is said. Speech may be evil even when it is true. Character assassination, insinuation, the spreading of suspicion, the sowing of unrest, derogatory talk, depreciation, back-biting and bad-mouthing are subtle ways in which the trust on which human relations depend is undermined. It is all the more dangerous since it is often done in private and denied in public. Its practitioners tell themselves they have done no harm: they did no more than tell the truth, and people ought to know the faults of others. The sages said that in biblical times leprosy was the punishment for evil speech (ibid.). The act done in private was thus exposed in public, and those guilty of it were shamed, and forced temporarily to live outside the camp as pariahs.
(Rabbi Sacks's commentary to Selichot for Maariv on Yom Kippur)