What exactly is a 'skill' in the context of using LLMs like Claude for accounting/tax work?

A 'skill' is essentially a document (like a markdown or Word file) that gets uploaded into an LLM's context to instruct it on exactly how to perform a specific task correctly, rather than letting it guess or hallucinate. Just as a human accountant has the skill of understanding British tax law, a 'skill' document gives an LLM the equivalent specialized knowledge for a given jurisdiction or task. One participant offered an analogy: asking an LLM 'what's the best pizza?' gives a broad, generic answer, but asking for 'the best Neapolitan-style, gluten-free pizza' gives a specific, useful answer — similarly, loading the right skill document before asking about tax reconciliation or 1040 prep produces a much more accurate, specific result than an unguided prompt. The purpose is to mitigate the risk of incorrect output by providing the LLM with verified, professionally-reviewed reference material before it's asked to compute something like a tax return.