对比 (duì bǐ) means to contrast, highlighting differences; it can also be a noun meaning 'contrast' or 'ratio'. Unlike 比 (bǐ), which compares degree (A比B大), or 比较 (bǐ jiào), which also means 'relatively', 对比 is about side-by-side contrast. 对照 (duì zhào) is for checking against a reference.