In English vocabulary, choose the correct one word substitute for "regular users or frequent customers of a place such as a restaurant".

Introduction / Context:
This one word substitution question is about the way we refer to groups of regular users or frequent customers of a business, such as a restaurant, hotel, or shop. In English, there is a special collective noun that describes all the customers who regularly support a particular establishment. Knowing such vocabulary helps in reading articles about business, tourism, and hospitality, and is a common topic in general English exams.

Given Data / Assumptions:

• The phrase describes regular users of places or restaurants.
• We are looking for a collective term, not a single person.
• Four options are provided, including one obvious collective noun.
• The context is commercial or service based rather than general frequency.

Concept / Approach:
The word clientele refers to all the clients or customers of a particular business, especially regular or important ones. It is a collective term, unlike client, which refers to a single person. The option often is an adverb of frequency and cannot name a group of people. Usage is a noun meaning the way something is used, not the people who use it. Therefore, clientele is the only option that correctly captures the idea of regular users of a place or restaurant.

Step-by-Step Solution:
Step 1: Notice that the phrase talks about regular users in the plural, not one individual. Step 2: Recognise that we therefore need a word that can function as a collective noun. Step 3: Recall that clientele means the group of customers of a business. Step 4: Compare each option and eliminate those that do not describe a group of people. Step 5: Select clientele as the one word that fits the given description.

Verification / Alternative check:
Use each option in a typical sentence such as The restaurant has a loyal ____ who come every weekend. Only clientele fits naturally: The restaurant has a loyal clientele who come every weekend. The sentence The restaurant has a loyal client changes the meaning to a single person. The restaurant has a loyal often or usage is clearly wrong and ungrammatical. This context based check confirms that clientele is the correct answer.

Why Other Options Are Wrong:
Client refers to a single customer or person who receives services, especially in professions like law, medicine, or business consulting, not to the whole group.

Often is an adverb describing how frequently something happens; it cannot stand for a group of people.

Usage describes the manner or frequency of use of something, such as language usage, and does not name people at all.

Common Pitfalls:
Learners sometimes confuse client and clientele, using client when they really mean the entire group. A simple memory tip is that words ending in ele or yle, like clientele and style, often suggest a broader pattern or group rather than one individual. In exam settings, always check whether the question is describing one person or many regular users before picking your answer.

Final Answer:
The correct one word substitute for regular users of a place or restaurant is Clientele.