Performance & Core Web Vitals · Glossary term

CLS (Cumulative Layout Shift) explained without jargon.

How much the layout "jumps" during loading (images without width/height, fonts appearing late, injected banners). Target: under 0.1.

← Back to glossary See Speed module →

Extended definition

How much the layout "jumps" during loading (images without width/height, fonts appearing late, injected banners). Target: under 0.1.

Context and application

CLS accumulates throughout the session — even a small fold shift (cookie banner appearing after 3 seconds, ad loading delayed) adds up. Most common causes: images without explicit dimensions (browser doesn’t reserve space), web fonts with FOIT/FOUT (text changing size when font loads), dynamically injected ads, cookie banners pushing content. Fix: width + height attributes on ALL images, font-display: swap + size-adjust on @font-face, CSS space reservation for ads and cookie banners with min-height.

In practice

set explicit width/height on images + use font-display: swap.

How SEO Master PRO MAX helps

For CLS (Cumulative Layout Shift), the relevant module in the app is Speed module. See the dedicated page for how it works concretely on your site.

See Speed module →

Related terms

Core Web Vitals, Image optimization.

Rest of the glossary

The SEO Master PRO MAX glossary has 58 essential terms, organized in 7 categories (Audit & Technical SEO · Content & On-page · Performance & Core Web Vitals · Backlinks & Authority · AI & Search 2026 · SERP, Schema & Rich Results · Privacy & Compliance). All with clear definitions, extended context, concrete examples.

← All 58 terms Category: Performance & Core Web Vitals

Now that you know what cls (cumulative layout shift) is, apply it on your site.

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