This is the 29th most frequent Bulgarian word.
във
The Bulgarian word "във" means "in" or "into" and is used before words starting with certain consonants for euphony.
Here, "във" is used to mean "on" when referring to a day of the week starting with "в" rhetorically to avoid repeating sound.
Трябва да отидем във вторник.
We must go on Tuesday.
Using "във" instead of "в" provides a more fluid and natural pronunciation when followed by a word starting with "ф".
Той работи във фирма за технологии.
He works in a technology company.
"Във" is preferable for smooth pronunciation before the name starting with the consonant cluster "Ве".