Short definition
A CMS is software that lets non-developers create, edit, and publish website content without touching code.
In depth
CMS options span a spectrum: monolithic platforms (Wix, Squarespace, WordPress) bundle hosting, editor, and templates; headless CMS systems (Sanity, Contentful) provide an editor and API only; site builders (Webflow, Framer) offer visual development with hosted CMS. Choosing depends on team skills, growth plans, and ownership requirements. Service businesses with serious SEO ambition usually outgrow Wix/Squarespace and adopt either WordPress or a custom front end + headless CMS.
Example
A service business outgrows Squarespace's SEO ceiling and migrates to WordPress, then later to Next.js + Sanity for full performance and design control.