The language of your files

File format glossary

Know what’s inside your files. Explore 39 plain-language explanations of image formats, PDF terminology, compression and data privacy.

39 terms

A

Aspect ratioImages: Aspect ratio is the relationship between an image’s width and height, usually written as two numbers such as 16:9.
AVIFImages: AVIF is a modern image format based on the AV1 video codec that produces very small files and supports transparency and HDR.

Base64also data URLFiles and data: Base64 is an encoding that represents binary data using text characters so it can travel through systems that expect text.
BMPImages: BMP is an early Windows image format that usually stores pixels uncompressed, producing large files that open almost anywhere.

Character encodingalso UTF-8, text encodingFiles and data: Character encoding is the rule a text file uses to turn letters and symbols into bytes. UTF-8 is the most common encoding today.
CSVFiles and data: CSV is a plain-text format that stores table rows as lines and separates the fields in each row with a delimiter, usually a comma.

Delimiteralso field separatorFiles and data: A delimiter is the character that separates one field from the next in a text data file, such as the comma in a CSV or the tab in a TSV.
DPIalso PPI, print resolutionImages: DPI, or dots per inch, is a print setting that says how many image pixels should fill each inch of paper. It doesn’t change the pixels themselves.

Electronic signaturealso e-signaturePDF and text: An electronic signature is any electronic mark a person adds to show they agree to a document, from a typed name to a drawn signature image on a PDF.
EXIFalso EXIF data, ExifPrivacy: EXIF is metadata stored in some image files that can describe camera settings, capture time, orientation and GPS location.

File extensionFiles and data: A file extension is the suffix after the final dot in a filename that commonly indicates its format, such as .jpg or .pdf.
File hashalso checksum, hash valuePrivacy: A file hash is a fixed-length value calculated from a file’s bytes using an algorithm such as SHA-256, used to check that a file hasn’t changed.
File signaturealso magic number, magic bytesFiles and data: A file signature is a fixed pattern of bytes near the start of a file that identifies its real format, regardless of the filename.

GIFalso animated GIFImages: GIF is an image format limited to 256 colors that supports simple animation and on-or-off transparency, best known for short looping clips.

HEICalso HEIFImages: HEIC is the photo format iPhones use by default. It stores images about half the size of an equivalent JPEG, but many programs and websites can’t open it.
Hex color codealso hex code, hex color, hex colourImages: A hex color code is a six-character value such as #1A73E8 that describes a color by its red, green and blue amounts in hexadecimal.

ICOalso faviconImages: ICO is the Windows icon format. One .ico file can hold the same icon at several sizes, which is why websites use it for their favicon.
Image orientationalso orientation tag, EXIF orientationImages: Image orientation is the direction a picture should be displayed. Photos often record it as a metadata tag instead of storing their pixels upright.

JPEGalso JPGImages: JPEG, often written JPG, is the most widely used photo format. It makes files small by discarding detail the eye is least likely to notice.
JSONFiles and data: JSON is a text format for storing structured data as objects, arrays and simple values, widely used by websites and apps to exchange data.

Lossless compressionalso losslessImages: Lossless compression reduces the space needed to store data while allowing the original to be recovered exactly, bit for bit.
Lossy compressionalso lossyImages: Lossy compression reduces file size by permanently discarding some information, aiming to keep the result looking or sounding similar.

MetadataPrivacy: Metadata is information about a file rather than its visible content, such as its author, creation time, image dimensions or camera settings.
MIME typealso media type, content typeFiles and data: A MIME type is a label such as image/png or application/pdf that tells browsers, email programs and servers what kind of data a file contains.

OCRalso text recognitionPDF and text: OCR, or optical character recognition, identifies text in images and scans and converts it into characters you can search, copy and edit.

PDFPDF and text: PDF is a document format designed to look the same on every device, preserving fonts, layout and images exactly as they were set out.
PixelImages: A pixel is a single square of color in a digital image. An image’s pixel dimensions, such as 1200 × 800, say how many it contains.
PNGImages: PNG is an image format that uses lossless compression and supports transparency, making it ideal for screenshots, logos and graphics.

QR codeFiles and data: A QR code is a square two-dimensional barcode that stores text, a web address or other data in a grid of dark and light modules.

Raster imagealso raster graphics, bitmap imageImages: A raster image is a picture made from a fixed grid of pixels. Photos, screenshots and scans are raster images, as are JPEG, PNG and WebP files.
Redactionalso redactPrivacy: Redaction is permanently removing sensitive information from a document or image before sharing it, not just covering it up.

SVGImages: SVG is a text-based image format that describes shapes, paths and text mathematically, so it stays sharp at any size.

Text layeralso searchable PDF, OCR layerPDF and text: A text layer is the real, selectable text inside a PDF. Without one, a PDF is only pictures of pages and its words can’t be searched or copied.
Transparencyalso alpha channel, transparent backgroundImages: Image transparency lets a background show through some or all of an image’s pixels, stored in an extra value per pixel called the alpha channel.

Vector graphicsalso vector image, vector fileImages: Vector graphics describe images as shapes, lines and curves defined by coordinates, so they can be scaled to any size without losing sharpness.

WatermarkImages: A watermark is text or a logo placed over an image or document to show ownership or status, such as a photographer’s name or the word DRAFT.
WebPImages: WebP is an image format made by Google for websites. It supports lossy and lossless compression and transparency in smaller files than JPEG or PNG.

XLSXalso Excel workbookFiles and data: XLSX is the standard Excel workbook format, storing sheets, formulas, formatting and data types in a compressed package of XML files.

ZIPalso ZIP archive, ZIP fileFiles and data: ZIP is an archive format that bundles files and folders into a single file and can compress their contents losslessly.