A plugin is just a bundle of MCPs, skills and templated prompts.

A skill cannot provide MCPs and can't provide custom template prompts, each skill is it's own slash command.

A plugin you can define N number of custom slash commands, and you can define MCPs as well as skills. So it bundles like all the things together.

By installing a plugin, you are basically installing a bunch of MCPs, skills and custom slash command prompts.