PascalCase capitalises every word including the first, with no separators: PageLoadTime, UserAccount, OrderSummary.
How it differs from camelCase
Only in the first character. userAccount is camelCase; UserAccount is PascalCase. The distinction is small and load-bearing in most languages.
Where it is the convention
Class and type names in C#, Java, TypeScript and most object-oriented languages. Component names in React and similar frameworks. Many schema and entity definitions.
Why the first letter carries meaning
In several languages the initial capital is not stylistic — it distinguishes a type from a variable, and in Go it controls whether a name is exported from its package.
Try it: Convert to PascalCase on SeoWolf's Notepad.