Jupiter in Jyotisha is Guru — literally 'the teacher' — also Brihaspati, priest of the gods. It governs expansion, wisdom, faith, meaning, children, wealth and merit. It's the greatest benefic of the nine, and not because it makes things better: it makes them larger and more meaningful — and what has meaning, people tend to feed.
Mechanically, Jupiter is at home in Sagittarius and Pisces, exalted in Cancer and debilitated in Capricorn. Cancer is nourishment: Jupiter at its best is compassionate wisdom. Capricorn is limit and hard reality: there its sense of meaning compresses into cost-benefit. It's a slow planet (about a year per sign), so Jupiter speaks to the long-term, the good that accrues over time.
Where you'll recognise it: wanting to teach, believing things mean something, generosity, a feel for philosophy or religion, particular care for children and students. Running well, Jupiter is your broadest part: conviction, scale, the ability to give, and a pull on resources. Stuck, it's excess — over-optimism, over-promising, 'believing' as a substitute for checking; or the reverse, meaning drained out and everything feeling pointless. Jupiter's lesson is that expansion needs roots: growing large is its nature; standing firm is another planet's job.
