Sampling is a process used to make inferences about a whole population by studying a representative subset. There are two main types of sampling: probability sampling, where every member has a known chance of selection, and non-probability sampling, where the probability of selection is unknown. Common probability sampling techniques include simple random sampling, stratified sampling, systematic sampling, and cluster sampling. Common non-probability techniques are judgment sampling, quota sampling, snowball sampling, and convenience sampling. The advantages of sampling include lower cost, faster results, and greater flexibility compared to studying the entire population.