mental preparedness; being braced for; being steeled for
Refers to the state of having mentally prepared oneself for something, often something difficult or unpleasant. Commonly used in expressions like 心の準備ができている (to be mentally ready) or 心の準備をする (to prepare oneself mentally).
You should prepare yourself mentally before hearing the bad news.
She wasn't mentally prepared to see the exam results.
準備 is general preparation (physical or mental), whereas 心の準備 specifically refers to mental or emotional readiness.
Compound of 心 (こころ, 'heart, mind') + の (possessive particle) + 準備 (じゅんび, 'preparation'). Literally 'preparation of the heart/mind'.