I never fail to confuse my non-developer coworkers when I talk about the differences between websites and web applications. This is because the definitions are murky and the differentiators can be less than clear.
Unfortunately, there is no industry-wide standard definition for either term, so I use the following rules of thumb:
In general, the main purpose of a website is for a visitor to consume content. Think of Chevron's website: you can read the company's history, download their annual report, and browse their press releases. The users' interactions almost all focus on passive content consumption.
In general, what distinguishes a web application from a website is that a web application focuses on data manipulation and user interactivity. Google Sheets falls squarely into the web application category: its purpose is to allow users to interactively create and manipulate spreadsheet data. It serves as a substitute for the desktop application Microsoft Excel.
While comparing Chevron's website to Google Sheets creates a clear distinction, it is rarely that obvious.
I've built many websites with WordPress, but WordPress itself is most definitely a web application. I still refer to the projects I've built using WordPress as websites.
Yet inside of websites, you can have embedded interactive experiences like custom map tools or quizzes. Even though these exist within a website, I would consider these individual widgets embedded web applications.
As if the distinction wasn't already murky enough, sites like YouTube, Facebook and Twitter blur it even further, as they exist both for serving and creating content. I consider these to be web applications, but I don't feel like it would be inaccurate to call them websites.
As a whole, the distinction between website and web application mostly only matters to developers. Sometimes, the distinction matters to my digital advertising coworkers, but only to the extent that it affects project timeline, budget, and how we implement tracking (some web applications require us to implement Google Analytics differently than a typical website).
If you're worried that you're confused by these distinctions, don't be: the distinctions aren't completely clear. Ninety-nine percent of the time, you can call anything in a browser a website and it'll be fine.