A person who has been granted a "Green Card" is a Lawful Permanent Resident of the United States. Two of the most common ways for a person to become a Lawful Permanent Resident is through family based and employment based sponsorship. Although having Lawful Permanent Residence has many benefits and is a way to live permanently in the United States, it does not have the same freedom and permanence as U.S. Citizenship.
Lawful Permanent Residents must permanently reside in the United States and therefore travel outside the country for certain periods of time may be limited. Additionally, lawful permanent residents may not vote in any federal, state, or local election that requires U.S. Citizenship. Lawful Permanent Residents must inform the government any time they move and also risk losing their permanent residency through extended absence from the United States, commission of certain immigration violations, and/or certain criminal convictions and pleas.
Individuals who obtain Lawful Permanent Residence through marriage to a U.S. Citizen when the marriage is less than two years old are placed in a two-year "conditional" category of Permanent Residence and MUST apply to remove those conditions prior to the two-year expiration, or they risk losing their "Green Card" and could be placed in deportation proceedings.