noun
irrespective of; without distinction; regardless of
Used in the pattern ...の別なく to mean 'without distinguishing between ...' or 'regardless of ...'. Often follows nouns like 年齢, 性別, 国籍, etc.
このイベントは年齢の別なく参加できます。
This event is open to all, irrespective of age.
性別の別なく、誰でも応募できます。
Anyone can apply, regardless of gender.
問わず is more common and versatile, meaning 'regardless of' or 'irrespective of', and can be used in a wider range of contexts. 別なく is more formal and often used in written or official language.
かかわらず means 'in spite of' or 'regardless of', but often implies a contrast or unexpected result. 別なく simply means 'without distinction' and is more neutral.
From 別 (べつ, 'distinction') + なく (adverbial form of ない, 'not'). Literally 'without distinction'.