Images
| 扩展名Ext | 全称Stands for | 一句话说明In one line |
|---|---|---|
| .jpg / .jpeg | JPEG | 照片通用格式，体积小，不支持透明Universal photo format; small, no transparency |
| .png | Portable Network Graphics | 支持透明、无损，截图和 logo 首选Lossless with transparency; screenshots & logos |
| .gif | Graphics Interchange Format | 动图老将，只有 256 色Animated veteran, 256 colours only |
| .webp | WebP | 谷歌出品，同画质比 JPG 小三成Google's format; ~30% smaller than JPG |
| .svg | Scalable Vector Graphics | 矢量图，放大不失真，网页图标标配Vector, infinitely scalable, web icons |
| .heic | High Efficiency Image Container | iPhone 默认格式，Windows 旧版打不开iPhone default; older Windows can't open it |
| .raw / .cr2 / .nef | Camera RAW | 相机传感器原始数据，后期空间最大Sensor data straight from the camera |
| .psd | Photoshop Document | Photoshop 工程文件，含图层Photoshop project with layers |
Documents
| 扩展名Ext | 全称Stands for | 一句话说明In one line |
|---|---|---|
| Portable Document Format | 跨设备排版不变，正式文件标准Fixed layout everywhere; the formal standard | |
| .docx | Office Open XML (Word) | Word 文档（新版），可编辑Word document, editable |
| .xlsx | Office Open XML (Excel) | Excel 表格（新版），带公式Excel workbook with formulas |
| .pptx | Office Open XML (PowerPoint) | 演示文稿Presentations |
| .txt | Plain Text | 纯文本，任何设备都能开Plain text, opens anywhere |
| .csv | Comma-Separated Values | 逗号分隔表格，数据交换通用Comma table; the data-exchange lingua franca |
| .md | Markdown | 轻量标记文本，写作用与笔记圈通用Lightweight markup; writers & notes |
| .html | HyperText Markup Language | 网页本体Web pages themselves |
Audio & video
| 扩展名Ext | 全称Stands for | 一句话说明In one line |
|---|---|---|
| .mp3 | MPEG-1 Audio Layer III | 音频通用格式，兼容性之王The audio everyone can play |
| .wav | Waveform Audio | 无损未压缩，体积大，录音棚用Uncompressed lossless; big files |
| .flac | Free Lossless Audio Codec | 无损但比 WAV 小，音乐发烧友首选Lossless yet compact; audiophile pick |
| .m4a | MPEG-4 Audio | 苹果生态音频，同码率优于 MP3Apple-ecosystem audio, better than MP3 |
| .mp4 | MPEG-4 Part 14 | 视频通用格式，手机相机默认The video everyone can play |
| .mov | QuickTime Movie | 苹果视频容器，剪辑软件友好Apple container; editor-friendly |
| .mkv | Matroska Video | 万能容器，多音轨字幕一锅端Everything-container: tracks & subtitles |
| .avi | Audio Video Interleave | 老格式，如今多见于老资源Legacy; mostly old downloads |
Archives, images & installers
| 扩展名Ext | 全称Stands for | 一句话说明In one line |
|---|---|---|
| .zip | Zip archive | 压缩包通用格式，系统原生支持The archive; native OS support |
| .rar | Roshal Archive | 压缩率高，解压需装 WinRAR 类工具Better ratios; needs a tool to open |
| .7z | 7-Zip archive | 开源格式，压缩率最高一档Open-source; top-tier compression |
| .tar.gz | Tarball + Gzip | Linux 世界标配的「打包再压缩」Linux's tar-then-gzip standard |
| .iso | ISO disc image | 光盘镜像，装系统和软件分发用Disc image for OS installs |
| .exe / .msi | Windows executable / installer | Windows 程序与安装包——双击即运行的类型Windows programs; runs on double-click |
| .apk | Android Package | 安卓安装包，装前确认来源Android installer; mind the source |
| .dmg | Apple Disk Image | macOS 安装镜像，Windows 打不开macOS image; not for Windows |
Renaming is not converting
The extension is just the label after the last dot; the file's internal structure is a separate thing. Renaming .png to .jpg swaps the label, not the data — the system decodes PNG bytes as JPG and you get errors or noise. Real conversion means decode-then-re-encode: images through a converter, documents saved out of their apps, PDF text through an extractor. When a file will not open or a system rejects it, identify the format first — renaming the suffix is the last thing, not the first.
The double-extension trap
"invoice.pdf.exe", "CV.docx.scr" — the real extension always sits after the last dot. Windows hides known extensions by default, so invoice.pdf.exe displays as invoice.pdf while double-clicking runs a program. Three defences: make extensions visible (File Explorer → View → tick "File extensions"; same in Finder's settings); treat any file with a dot after the dot as suspicious; never double-click unknown .exe, .msi, .scr or .bat files. Phones are safer, but the same rule applies to unknown .apk files.
FAQ
I cannot see file extensions — how do I show them?
Windows 11: File Explorer → View → Show → tick "File name extensions". Windows 10: the View tab → tick "File name extensions". macOS: Finder → Settings → Advanced → "Show all filename extensions". Keep this on permanently — the double-extension trap becomes instantly visible.
Does case matter? Is .JPG the same as .jpg?
For your operating system, no — Windows and macOS are case-insensitive and .JPG opens fine. Exceptions exist: some web servers map extensions to MIME types case-sensitively, and strict scripts match exactly. If an upload rejects your file for format, try an all-lowercase extension first.
How do I turn .heic photos into .jpg?
Run a real conversion: the <a href="image-converter.html">image converter</a> does it locally — drop the file in, choose JPG output. Or switch the iPhone camera from "High Efficiency" to "Most Compatible" so new shots are JPG natively; existing photos still need converting.