dying; laying down one's life
Formal or literary term for death, often implying a noble or sacrificial death. Not used in casual conversation.
He died for his country.
With one out and the bases loaded, the batter struck out.
一死 means "one out" while 二死 means "two outs"; the two are easy to mix up since they share the same 死 form and only differ by the out count.
Compound of 一 (one) and 死 (death). The baseball sense is a specialized extension of the literal meaning.