A: I'm very hungry.

B: Let's go to the restaurant then.

(In this sentence, what is the use of 'the' before 'restaurant'? Does it refer to the specific restaurant or is 'the' used in generic usage?)

If "the" is used, it is more specific. If "a" is used, then it is more generic.

In the sentence "Let's go to the restaurant then," the use of 'the' before 'restaurant' indicates that the speaker is referring to a specific restaurant. In this case, it suggests that there is a particular restaurant in mind that both parties are aware of or have previously discussed.

To determine if 'the' is being used in a generic sense or referring to a specific restaurant, you can consider the context of the conversation. If the speaker had said "Let's go to a restaurant then," it would suggest a general or non-specific restaurant. However, the use of 'the' indicates a particular establishment that is known to both the speaker and the listener. This could be a restaurant they have previously mentioned or a specific one they have in mind.

Remember that the use of definite article 'the' implies specificity, whereas the use of the indefinite article 'a/an' suggests a more general or non-specific reference.