Noun
soft sign (plural soft signs)
The Cyrillic letter Ь/ь (transliterated in English with an apostrophe (’) or prime (′)), which in modern languages using the Cyrillic alphabet serves to denote a soft (palatized) consonant.
Synonyms: front jer, front yer
Antonym: hard sign
Names that end in -я acquire a soft sign in this case: "Оль!" Source: Internet
These iotated vowel letters and a special soft sign change a preceding consonant from hard to soft. Source: Internet