Simple definition
A WordPress theme defines the site presentation, templates and visual design.
Technical definition
Themes supply templates, styles and optional theme functions. Block themes use site-editing templates and theme.json; classic themes typically use PHP templates. A child theme can preserve customizations during parent-theme updates.
What is it used for?
Customize site appearance without modifying WordPress core or unrelated plugins.
Practical example
Use a child theme for custom styling or template changes, then test responsiveness and compatibility after updating the parent theme.
Common issues
- Plugin or theme conflict
- Incompatible update
- Cache hiding the change