日后 (rì hòu) is a formal, written term meaning 'someday in the future' — it refers to an indefinite, unspecified future time, often used in plans or predictions. Unlike 以后 (yǐ hòu), which can mean 'after' a specific event or time, 日后 is more abstract and literary. It is similar to 将来 (jiāng lái) but 将来 is a broader noun for 'the future' as a concept.