When people refer to an “X file,” they typically mean a file whose name ends in `.x`, the suffix after the last dot such as in `model.x`, which helps Windows or macOS guess what program should open it, similar to how `.pdf` or `.zip` identify their file types, though this system isn’t foolproof since extensions can be changed or reused for completely different formats.Because a `.x` file can belong to different ecosystems—often either an older DirectX 3D mesh format or a Lex lexer definition—the quickest identification method is to check its source and view it in a text editor to look for DirectX signatures such as `xof 0302txt` alongside meshes and numeric lists, or for Lex-like syntax that includes `%%` dividers or `% ... %` code snippets.If X format appears as nonsense in Notepad, it may be a binary version, and you can still try searching for readable hints inside it such as `TextureFilename` for DirectX-style content or rule-based terms for Lex-related material, and it’s also wise to confirm that Windows is showing actual extensions through File Explorer → View → “File name extensions,” since a file that seems to be `something.x` might really be `something.x.txt` or even `something.x.exe`, which affects how you should treat it.A single extension like `.x` ends up with multiple meanings because file extensions are human-made shortcuts, not globally governed identifiers, which means any group can adopt the same suffix—letting `.x` serve DirectX model formats in 3D pipelines while also representing lexer source files in development tools—something that happens frequently with short extensions whose limited pool encourages collisions.Another reason is that an extension typically identifies a general format family rather than one strict schema, and many formats include both text-based and binary flavors, so `.x` files can look drastically different even inside one workflow; combined with Windows’ reliance on extension-based associations instead of reading the file’s structure, a `.x` file may open in a 3D viewer on one computer and a text editor on another, and because extensions can be renamed without changing the underlying data, mismatches between label and content are common.Because of all that, the best way to identify a `.x` file in your situation is to use context plus a fast content inspection by opening it in a text editor and searching for meaningful headers or terms, and if you provide the first 10–20 lines or say which program it came from, I can tell you precisely which `.x` format you have.The reason `.x` can denote unrelated formats is that extensions are loosely controlled identifiers, so two independent communities can select the same one-letter suffix without conflict, and because operating systems rely on associations rather than deep inspection, a `.x` file can open in a 3D application on one system and a text editor on another, making its meaning appear inconsistent.Some `.x` formats appear in different forms, including text and binary versions, meaning two related `.x` files can look nothing alike in a text editor, and since extensions can be changed so easily, you may find files where the extension doesn’t match the real data, making context and a brief content check the most reliable way to determine what `.x` type you have.