A balanced mic is based on a balanced connection offering better rejection to outside noise by a phenomenon known as CMR, common mode rejection. For example, audio is AC at an…y moment at any single place on a twisted pair balanced cable, the audio is both +5 and - 5 V. If external noise is inducted on to the cable at, say +1 V, that +1 V is added to the + 5 and the - 5. As an arithmetic trick of elementary electronics, the noise is cancelled out inside the circuitry of the next stag.
In other words, a balanced mic helps to elimate noise balancing the audio output. Unbalanced means it has less power, meaning it may produce more erroneous noise..