In Japanese, the symbol 々 is used in any kind of writing. In Chinese, it is sometimes used in casual horizontal writing (or calligraphy) to indicate a repeated character, but not in formal writing, in print. More often, 〻 is used (but still only casually), or sometimes the older 二. Usually, however, the character is simply written twice, without the use of any of the above symbols.
In Japanese, this mark is formally called 漢字返し(kanji-gaeshi, “kanji repeater”) or 同の字点(dō no ji ten, “same-character mark”). More casually, it is called noma since it looks like a combination of the katakana ノマnoma, 繰り返し(kurikaeshi, “repeating”), 同じ(onaji, “same”), or 同じく(onajiku, “same”).