expression, noun
Herculean task; next-to-impossible undertaking
Describes a task or feat that is extremely difficult, almost impossible to achieve.
この難問を解くのは至難の業だ。
Solving this difficult problem is a Herculean task.
彼は至難の業を成し遂げた。
He accomplished a next-to-impossible undertaking.
至難 (extremely difficult) + の (possessive particle) + 業/技 (task, feat). The phrase literally means 'a task of extreme difficulty'.