An immigration bond is what a person pays the Department of Homeland Security to release an individual who is in immigration detention.  People generally get placed in immigration detention when they are caught entering the United States illegally or have done something to violate their legal status in the United States, such as committing a crime or overstaying a Non-Immigrant Visa.  When somebody is detained for violating an immigration law, the government will evaluate whether they are eligible for a bond.  Some people who have committed serious crimes can be subjected to mandatory detention which means they are ineligible for a bond.  Aside from people with a serious criminal background, mandatory detention under INA § 236(c) can be applied to people who have just arrived in the United States at a border or other point of entry, and have no legal basis for being here.  Depending on a number of factors, these people may be ineligible for a bond unless they can prove that they have a Credible Fear for returning to their home country.  Credible Fear means that they have the possibility of becoming eligible for asylum and if they can prove this to a USCIS Asylum Officer, they may be eligible for a bond.  A bond is not available to a person who has criminal issues that make them ineligible or if they are considered arriving aliens and cannot prove that they have a credible fear of returning to their home country.