What exactly are AI SKILLS, and how should they be applied?

AI tools are widely used now, and people keep hearing about this SKILL or that SKILL.
So what exactly are they, how can they assist people in using AI tools, and how should these SKILLS be used?
These are all thought-provoking questions.

Skill Definition:
A Skill is an operation manual for AI, telling it: "In what situations to use this method and tool, and how exactly to do it."
The true core lies in: how to enable an Agent to have "task planning ability"...
In other words, it's about giving AI an "expert brain," so AI can think like an expert, automatically follow rules, and produce stable, controllable outputs:
Understand user intent → plan workflow → choose execution path → process data transfer → handle exceptions.

In simple terms:
Agent Skill = a packaged "professional capability module" for AI.

It is not just a prompt, but a complete set of work rules and scripts that can be loaded, triggered, and reused.
Although AI agents are extremely capable, they know nothing about your project.

For example:
"How does this team write commit messages?"
"What frontmatter format does this blog use?"
"What commands are used during deployment?"
Without Agent Skill, the AI cannot know these details.

Agent Skill allows the AI to understand "the correct way to do these things" before taking action.