1. language acquisition: It refers to the child’s acquisition of his mother tongue, i.e. how the child comes to understand and speak the language of his community.

2. language acquisition device (LAD): A hypothetical innate mechanism every normal human child is believed to be born with, which allow them to acquire language. (03)

3. Universal Grammar: A theory which claims to account for the grammatical competence of every adult no matter what language he or she speaks.

4. motherese: A special speech to children used by adults, which is characterized with slow rate of speed, high pitch, rich intonation, shorter and simpler sentence structures etc.----又叫child directed speech，caretaker talk.(05)

5. Critical Period Hypothesis: The hypothesis that the time span between early childhood and puberty is the critical period for language acquisition, during which children can acquire language without formal instruction successfully and effortlessly. (07C/ 06F/ 04)

6. under-extension: Use a word with less than its usual range of denotation.

7. over-extension: Extension of the meaning of a  word beyond its usual domain of application by young children.

8. telegraphic speech: Children’s early multiword speech that contains content words and lacks function words and inflectional morphemes.

9. content word: Words referring to things, quality, state or action, which have lexical meaning used alone.

10. function word: Words with little meaning on their own but show grammatical relationships in and between sentences.

11. taboo: Words known to speakers but avoided in some contexts of speech for reasons of religion, politeness etc. (07C)

12. atypical development: Some acquisition of language may be delayed but follow the same rules of language development due to trauma or injury.