In plain English
A skill is a saved set of instructions an AI loads when a task needs it. Context is everything the model can read while it works on a task. A Gemini Gem is a saved Gemini assistant with its own instructions.
On 2 October I posted Stupid Gemini Tricks, a Gemini Gem I built for a U of Digital AI accelerator training. It makes a one-panel cartoon in the style of the New Yorker or The Far Side, and it took about two hours and a lot of iteration to get the prompt and context right.
The skill is the doing: the instructions for building the thing. The Gem's instructions say "Act as a veteran magazine gag cartoonist and creative editor," then tell it to pitch two or three concepts or punch up a gag the user already has, confirm the style, and then generate the image with the caption beneath the panel. Anthropic's documentation for Agent Skills says that "unlike prompts (conversation-level instructions for one-off tasks), Skills load on demand, so you don't have to repeat the same guidance across conversations."
The context is the contents: the things that go into a particular job. The Gem carries a style reference guide, with the New Yorker's "dip-pen and black ink with soft watercolor/wash shading" and the Far Side's "1980s retro muted print tones." The user brings the topic or the gag.
The context is the ingredients on the counter, the skill is the recipe card, and the model is the cook.
Anthropic defines skills as "reusable, filesystem-based resources" that hold "workflows, context, and best practices", so the style guide can travel with the skill. When Claude loads a skill, its instructions enter the context window too.