Something bad that is relentless never stops or never becomes less intense.
The pressure now was relentless.
压力现在毫无减弱之势。
Someone who is relentless is determined to do something and refuses to give up, even if what they are doing is unpleasant or cruel.
Relentless in his pursuit of quality, his technical ability was remarkable.
由于对质量的坚持不懈的追求,他的技术能力非同凡响。