All the words and phrases used in a particular language or subject; All the words and phrases used and known by a particular person or group of people.
Where as vocabulary is just words.
Examples:
- The lexicon of football includes terms such as linesman, friendly match, yellow card, penalty shootout, pitch, result, and draw.
- The lexicon of a stock trader includes terms such as delayed quotes, futures contract, limit order, margin account, short selling, stop order, trend line and watch list.