阳 is a bound form (语素) — it cannot stand alone as a word and always appears inside two-character compounds. Its most common meanings are 'the sun' (太阳, 阳光) and the yang principle in Chinese philosophy (阴阳 theory), which stands for positive, active, male, bright, and overt qualities — the opposite of 阴. You'll also see it in words like 阳性 ('positive' in medical tests, or 'masculine' in grammar).