Fetching details from the dictionary...
candid advice; frank advice; honest opinion; exhortation; harsh but honest advice
上司が部下に苦言を呈した。
The boss gave frank advice to the subordinate.
苦言を聞き入れる度量が要る。
It takes generosity to accept frank advice.
彼の苦言には一理ある。
His candid advice has a point.