Snippets are small bits of reusable template or tag parts in ExpressionEngine 2, renamed Template Partials in later versions.

Snippets are small bits of reusable template or tag parts. You could create a Snippet for any number of purposes, anywhere that you need to reuse a small portion of a template, including partial or complete tags, other variables, etc. Snippets add flexibility and reusability, while making it simple to make site-wide changes by editing the Snippet’s source instead of having to modify many templates.

https://docs.expressionengine.com/v2/templates/globals/snippets.html

They have been renamed Template Partials since ExpressionEngine version 3.

https://docs.expressionengine.com/latest/templates/globals/template_partials.html