loss of principal; falling below par value
Finance term for when the value of an investment drops below the original invested amount.
This investment trust carries the risk of loss of principal.
The stock price fell and I ended up with a loss of principal.
含み損 is an unrealized loss on paper, whereas 元本割れ emphasizes that the current value is below the original investment amount.
Compound of 元本 (principal) and 割れ (breaking, falling below), literally 'principal breaking'.