The Yom Tov of Erev Yom Kippur:[1]

From the letter of the law Erev Yom Kippur is not considered a Yom Tov at all.[2] Nevertheless, it is customary to treat it like a Yom Tov.[3] [It is for this reason that Erev Yom Kippur contains various laws similar to a Yom Tov, such as the omission of Tachanun, as will be explained.]

Is the night of Erev Yom Kippur also considered a Yom Tov:[4] This matter is dependent on the custom of the community. Some communities are accustomed to consider it a Yom Tov from the beginning of the night of Erev Yom Kippur. Others however only consider it a Yom Tov beginning from the morning [Alos] of Erev Yom Kippur.[5] According to all opinions, the Yom Tov of Erev Yom Kippur does not begin until the night of Erev Yom Kippur, and not from the Mincha prior on the 8th of Tishrei.[6]

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[1] Admur 604/4: “Although from the letter of the law Erev Yom Kippur is permitted in Hesped, being it is not a Yom Tov at all and does not contain advantage over other days other than it being a Mitzvah to eat on this day, nevertheless the custom is to treat it like a Yom Tov.”

[2] Admur ibid; M”A 607/10

[3] Admur ibid; Rama 570/1; Magen Avraham 570/6; M”B 570/8 that Erev Yom Kippur is referred to by people as a Yom Tov

[4] 604/4-5; Rama 604/2

[5] The practical ramifications regarding this matter is regarding decreasing in Selichos [604/4] and eating meat [604/5]

[6] 604/5; M”A 604/1

The proof: As Tachanun is recited during Mincha of Erev Yom Kippur while by other Yomim Tovim in which Tachanun is omitted, Tachanun is omitted even during the Mincha prior. From here we see that people only begin to consider Erev Yom Kippur as a Yom Tov from Tzeis Hakoachavim and onwards. [604/5]