What is the difference between undercoverage and nonresponse bias?

Undercoverage bias happens when segments of the target population are entirely excluded or less represented in the sample than they are in the population. This means that these segments are excluded from the sampling process.

Nonresponse bias occurs when parts of the sampled population are unable or refuse to respond. In other words, nonrespondents are included in the sampling process, but their answers (responses) are not registered.