Affixation is the formation of words by adding derivational affixes to different bases. It involves different degrees of derivation and debatable problems in prefixation, as well as the classification of prefixes and suffixation. The lecture also covers topics such as polysemy, homonymy, synonymy, and productivity. It discusses the synchronic approach of conversion, typical and semantic relations, basic criteria of semantic derivation, and the diachronic approach of conversion.