Having lost both father and mother, alone and without support.
Tips
history
From the Shijing (《诗经·小雅·蓼莪》): 无父何怙,无母何恃 ('without a father, on whom to lean? without a mother, on whom to rely?'). 失怙 (shīhù) means losing one's father; 失恃 means losing one's mother. The two are still paired in formal obituaries today.
register
Highly literary. In modern speech you would say 妈妈去世了 (māma qùshì le). 失恃 belongs to obituaries, family histories, and classical-flavored writing.