Word count is the number of words in a piece of text. The most common definition counts every whitespace-separated token: numbers, hyphenated compounds, and contractions all count as one word. Most word processors (Microsoft Word, Google Docs) and academic counters follow this convention.
Different specialised contexts use different rules: some legal counters split hyphenated compounds; some translation tools exclude numbers; copywriting tools sometimes exclude one- or two-character "stop words". When in doubt, use the convention your destination platform uses.