This is a common interview question for Jr. Developer roles and honestly just something all developers should know. Here's a secret though, interviewers aren't looking to see if you know the definition. They want to see how you explain it. This question test your technical communication skills. The interviewer wants to know, "Can you clearly present a project to developers and clients?" Here's how you can knock this question out.
A CRUD App is an application that lets users Create, Read, Update, and/or Delete content.
Simple and sweet but only the beginning. At this point the interviewer knows you can memorize a Google definition. Now you need to show understanding.
So let's say you have a blog. You as a user can Create/Publish a post, Read/Show your post, Update/Edit your post and Delete your post. Blogs are classic CRUD apps.
Now the interviewer knows you understand the concept but we can take this one step further to make the answer more complete.
In web development CRUD functionality is tied to API calls that updates the user's information in a database. Create is tied to a POST request, usually through a submit or publish button. Read ties to GET requests. Update ties to PUT and PATCH requests. Delete ties to DELETE requests.
There you have it. Now we have answered the question, shown that we understand our answer, and shown that we know why it was asked in the first place. If you have an interview coming and don't understand something I've written here, feel free to leave a comment and I'll discuss this with you.