1. CODE/ CODE SWITCHING

2. code-switching is the concurrent use of more than one language, or language variety, in conversation.
code-switching is the use of more than one linguistic variety in a manner consistent with the syntax and phonology of each variety.

3. Multilinguals - people who speak more than one language - sometimes use elements of multiple languages in conversing with each other.

4. A loanword (or loan word) is a word borrowed from one language and incorporated into another.
A calque or loan translation is a related concept where the meaning or idiom is borrowed rather than the lexical item itself..

5. A pidgin
A pidgin ( /ˈpɪdʒɪn/), or pidgin language, is a simplified language that develops as a means of communication between two or more groups that do not have a language in common
. A pidgin is not the native language of any speech community, but is instead learned as a second language. A pidgin may be built from words, sounds, or body language from multiple other languages and cultures. Pidgins usually have low prestige with respect to other languages.

6. A Creole
is a stable natural language developed from the mixing of parent languages; creoles differ from pidgins in that they have been nativized by children as their primary language, making them have features of natural languages that are normally missing from pidgins.
The vocabulary of a creole language consists of cognates from the parent languages, though there are often clear phonetic and semantic shifts.

7. Language transfer
Language transfer (language interference) refers to speakers or writers applying knowledge from their native language to a second language.

8. Code mixing
Code mixing is a thematically related term, but the usage of the terms code- switching and code-mixing varies. Some scholars use either term to denote the same practice, while others apply code- mixing to denote the formal linguistic properties of said language-contact phenomena, and code-switching to denote the actual, spoken usages by multilingual persons.

9. Social motivations for code-switching
Code-switching relates to, and sometimes indexes social-group membership in bilingual and multilingual communities. Some sociolinguists describe the relationships between code-switching behaviors and class, ethnicity, and other social positions. In addition, scholars in interactional linguistics and conversation analysis have studied code-switching as a means of structuring talk in interaction.

10. diglossia
, diglossia ( /daɪˈɡlɒsiə/; two languages) refers to a situation in which two dialects or languages are used by a single language community. In addition to the community's everyday or vernacular language variety (labeled "L" or "low" variety), a second, highly codified variety (labeled "H" or "high") is used in certain situations such as literature, formal education, or other specific settings, but not used for ordinary conversation

11. Convergence
Convergence - is a type of contact- induced change whereby languages with many bilingual speakers mutually borrow morphological and syntactic features, making their typology more similar.

12. Mechanics of code-switching
Code-switching mostly occurs where the syntaxes of the languages align in a sentence; thus, it is uncommon to switch from English to French after an adjective and before a noun, because, in French, adjectives usually follow nouns. Even unrelated languages often align syntactically at a relative clause boundary or at the boundary of other sentence sub-structures.

13. Borrowing / code-switching;
the difference between borrowing (loanword usage) and code-switching; generally, borrowing occurs in the lexicon, while code-switching occurs at either the syntax level or the utterance-construction level.

14. Some proposed constraints are
The Free-morpheme Constraint: code-switching cannot occur between bound morphemes.
The Equivalence Constraint: code-switching can occur only in positions where "the order of any two sentence elements, one before and one after the switch, is not excluded in either language." Thus, the sentence: "I like you porque eres simpático." ("I like you because you are nice.") is allowed because it obeys the relative clause formation rules of Spanish and English.
The Closed-class Constraint: closed class items (pronouns, prepositions, conjunctions, etc.), cannot be switched.
The Matrix Language Frame model distinguishes the roles of the participant languages
The Functional Head Constraint: code-switching cannot occur between a functional head (a complementizer, a determiner, an inflection, etc.) and its complement (sentence, noun-phrase, verb- phrase).

15. Types of switching
Scholars use different names for various types of code-switching.
Intersentential switching occurs outside the sentence or the clause level (i.e. at sentence or clause boundaries).[27] It is sometimes called "extrasentential" switching.
Intra-sentential switching occurs within a sentence or a clause.
Tag-switching is the switching of either a tag phrase or a word, or both, from language-B to language-A, (common intra-sentential switches)
Intra-word switching occurs within a word, itself, such as at a morpheme boundary.