What is the difference between lossy and lossless?

Lossy compression permanently discards some pixel data to achieve much smaller files. Lossless compression discards nothing — the decompressed image is identical to the original, so files stay larger. Use lossy for photographs, lossless for graphics, logos and screenshots.

What image format should I use?

For web use in 2026: AVIF first for the smallest files, WebP as the universal default, JPEG only for maximum compatibility (email, legacy systems), and PNG only for pixel-perfect flat graphics or hard transparency.

What are Core Web Vitals?

Google's three page-experience metrics measured from real Chrome users: LCP (Largest Contentful Paint) for loading, INP (Interaction to Next Paint) for responsiveness, and CLS (Cumulative Layout Shift) for visual stability.

Image compression & format glossary

Plain-English definitions for the terms used across our guides and in image compression generally. Each definition is a standalone page, so you can link to it directly.

How to use this glossary

Terms are cross-linked throughout the guides. Each one opens a dedicated page with a concise definition, practical notes on when it matters, and links to related guides.

All terms

8 terms defined and growing. If a term you need is missing, it's on our list — the related guides cover most concepts in depth meanwhile.

AVIF WebP Lossless compression Core Web Vitals MozJPEG Chroma subsampling Entropy coding Lazy loading

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Frequently asked questions

Image compression reduces the file size of an image while keeping it usable. Lossy compression (JPEG, WebP, AVIF) discards data the eye rarely notices for much smaller files; lossless compression (PNG, OxiPNG) discards nothing and reconstructs the original exactly.