Cyrillic Small Letter E

It represents a plain e vowel.

The backwards e is a vowel letter. In Russian, э keeps a preceding consonant hard when that consonant has both hard and soft versions. The everyday letter е can instead soften that consonant, or add a y sound at the start of a word. In это, э opens the word directly with the vowel; in мэр, it follows a hard m.

Why does э look backward?

Its shape has a long history, but no settled single origin.

Early forms appear in Serbian and, less often, Bulgarian writing of the 13th–14th centuries, often small and written above the end of a line. One explanation links the form to Glagolitic, an early Slavic alphabet; another links some East Slavic uses to the Hebrew letter aleph. Both are proposals, not a settled ancestry for the modern letter.

Silvester’s Miscellany, a handwritten collection of texts, uses the form in the name “El” from the late 14th or early 15th century. Related forms also occur in Russian Bible and chant manuscripts. Nonreligious examples complicate any explanation based only on religious writing.

Can I replace э with е?

No; Russian spelling is not a free choice between them.

In Russian loanwords the sound alone does not decide: бизнес and кафе are written with е after a hard consonant, while рэп and пленэр take э. Belarusian writes э much more regularly after hard consonants, so its spelling follows a different pattern.