Vocabulary is the number of words you know. Learners have an Active Vocabulary which are the words they use when they speak or write; they also have a Passive Vocabulary which are the words they may well understand but do not actively use.
For more, see Vocabulary and TEFL.
Verbs tell us about an action; they are sometimes called doing words or action words. Verbs describe what is happening:
run, walk, read, talk
For more, see Verbs in English Grammar,
TEFL stands for Teaching English as a Foreign Language. Simply put, this is usually used to talk about teaching English to people who live in a non-English speaking country and who want to learn English for business or to take an exam, etc.
It is pretty much equivalent to TESOL and TESL.
For more, see TEFL - Teaching English as a Foreign Language.
In linguistics, the term Language Register is used to talk about the type of language a person might use in a certain social context, in other words, how formally they will speak.
- A speaker might say I never done nuffin’ when talking to their friends, but when presented before the Queen that same speaker may well change the way they speak and say I have never done anything.
- A barrister will use a certain set of vocabulary or jargon in their formal work in court and a completely different set when they are explaining the same case to their lay friends at a dinner part the same evening.
- An English teacher may talk to their colleagues about verbs but talk to a class of 7 year-old children about doing words.
No register is right or wrong per se. What determines this is how appropriate the language used is in a certain situation.
Suppose as a teacher a student asks about the meaning of the word cop. It is simple to explain that the meaning is police officer but it is used in certain situations or as part of a certain register. An individual might refer to a police officer whilst giving a formal statement to the police: Three police officers arrived in a car ten minutes later. However, later when speaking to their friends, the same individual might say: Three cops turned up in their car ten minutes later.
Thus, register depends on:
- the speaker’s status
- the listener’s status
As a general TEFL teacher the most common reason register comes up is when dealing with what language is suitable in formal vs informal situations.