Frankness or candor; speaking plainly without beating around the bush. Can be used positively or negatively depending on context.
率直な意見を聞かせてください。
Please tell me your candid opinion.
彼の率直さが皆に好かれている。
People like him for his frankness.
率直に言えば、その案には賛成できない。
To be frank, I can't agree with that proposal.