An SEO glossary of terms every marketer should know in 2026
A practical, current glossary covering the essential SEO terminology every marketer should be comfortable with, from foundational concepts to 2026-specific terms.
6 min read
Unoptimised images remain the single most common cause of slow-loading pages across the web, and the fix is often straightforward: proper compression and modern format selection, without needing to touch anything else about the page's underlying code.
Why images cause the biggest speed problems
A single unoptimised photo straight from a modern camera or phone can be several megabytes — many times larger than an entire page's HTML, CSS and JavaScript combined — making image optimisation disproportionately impactful compared to almost any other single technical fix.
Modern formats worth adopting
- WebP: broad browser support, significantly smaller file sizes than JPEG or PNG at comparable visual quality.
- AVIF: even better compression than WebP in many cases, with growing but not yet universal browser support.
- Always provide a JPEG or PNG fallback for older browsers lacking modern format support.
Most sites are running years-old, unoptimised JPEGs and PNGs when a simple format and compression update would cut file sizes dramatically with no visible quality difference to a real visitor.
Compression without visible quality loss
Lossy compression at a reasonable quality setting (typically 70-85% for JPEG-equivalent formats) produces file sizes dramatically smaller than an uncompressed original, with no visible difference to most viewers — the visual quality loss only becomes noticeable at much more aggressive compression levels.
Sizing images correctly for their actual display dimensions
Serving a 3000-pixel-wide image to display in a 400-pixel container wastes enormous bandwidth — use responsive images (srcset) to serve appropriately sized files matching the actual display context across different devices.
Frequently asked questions
Will image compression noticeably hurt visual quality?
At reasonable compression levels (typically 70-85%), the difference is generally imperceptible to most viewers, while file size reductions can be substantial — extreme compression is where visible quality loss becomes a real concern.
Should I convert every existing image to WebP or AVIF?
Yes, for any actively used image, with an appropriate fallback for older browsers — the file size benefits generally outweigh the modest implementation effort required.
Do image compression tools work automatically as part of a CMS?
Many modern CMS platforms and plugins offer automatic compression and format conversion on upload, which is worth enabling if available rather than relying on manual compression for every image.
If your site's images need optimisation, talk to our team for a technical review.
The takeaway
Convert your largest, most-viewed images to WebP or AVIF with proper compression — this single change typically produces the largest file size reduction available without any visible quality loss.
Written by Fibvo — Bengaluru and Erode, India — working with clients in other time zones. Questions, or think we have it wrong? Tell us.
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