This document provides definitions and explanations of key concepts related to grammar and lexis. It defines grammar as how words are combined, changed and organized to make meaning. Grammar involves parts of speech, grammatical structures using prefixes, suffixes, and affixes. Lexis is defined as individual words or sets of words that have a specific meaning. Lexis involves the meaning of words, their forms, relationships between words like synonyms and antonyms, and contexts that determine word meaning. The document emphasizes the importance of these concepts for language teaching in the classroom.