A visa is a temporary authorization to enter and stay in the United States for a specific purpose and limited period of time. Types include tourist visas (B-1/B-2), work visas (H-1B, L-1), student visas (F-1), and many others. Visa holders must comply with the terms of their specific visa category, including departure before the visa expires.
A green card (permanent resident card) grants the holder lawful permanent resident status, allowing them to live and work in the United States indefinitely. Green card holders can travel freely in and out of the country (with some limitations on extended absences), work for any employer, and eventually apply for U.S. citizenship.
Key differences:
Visas are temporary; green cards are permanent.
Visas restrict you to specific activities (work, study, tourism); green cards allow you to live and work freely.
Visa holders must leave when their status expires; green card holders can stay indefinitely as long as they maintain their status.
Green card holders can apply for U.S. citizenship after 3-5 years; visa holders generally cannot (they must first obtain a green card).