adverb, noun
Often used in negative constructions (e.g., 並々ならぬ) to emphasize that something is beyond ordinary; can also appear in adverbial form 並々と.
彼の努力は並々ならぬものがあった。
His efforts were extraordinary.
並々の人間にはできない仕事だ。
It's a job that an ordinary person cannot do.
Less common variant without the repetition mark; still encountered.
普通 is the most common word for 'ordinary' or 'normal' and is used in a wide range of contexts. 並々 is more emphatic and often appears in negative or contrastive expressions to stress that something is not ordinary.
並 means 'average' or 'mediocre' and is often used as a suffix (e.g., 人並み). 並々 is a reduplicated form that intensifies the meaning, typically used in set phrases.
Reduplication of 並 (なみ, 'average, ordinary'), emphasizing the quality of being ordinary. The exact historical derivation is uncertain, but the form is well-established in classical and modern Japanese.