Many historians, sociologists and political scientists have different definitions and explanations about the term "carceral state." In his book Discipline and Punish: The Birth of the Prison (1975), French philosopher and historian Michael Foucault introduces the term "carceral archipelago," which roughly means "a society divided into prisons, jails and gated communities." Thus, a carceral state is, basically, a state constructed on the concept of incarceration, with the purpose of controlling the "urban space" via the use of various surveillance technologies and techniques.
In 2016, in a podcast interview conducted by Dissent (a political and cultural magazine), author and assistant professor of History and African and African American Studies at Harvard University Elizabeth Hinton claims that
The formal definition [of a carceral state] is that it’s the law enforcement officers who police the streets and help maintain order—it’s the court marshals, the lawyers, the probation and parole officers and, of course, correctional officials. So, it’s all the formal institutions of the criminal justice system. But the way that I think about the carceral state has been deeply informed by Foucault’s idea of the carceral, which is a carceral continuum or carceral network.
Some social theorists, however, argue that the definition should not be limited to law enforcement and prisons only, and should also include the private security sector, The Department of Homeland Security, the US Immigration and Customs Enforcement, and even the US Armed Forces, as well as those who provide various security and surveillance goods and services.
Ella Josephine Baker (1903–1986) was a human rights and political activist who became one of the most prominent figures of the 1950s and 1960s Civil Rights Movement. In 1957, she co-founded and organized Dr. Martin Luther King’s organization called the Southern Christian Leadership Conference (SCLC) and helped with the creation of the Student Nonviolent Coordinating Committee (SNCC) in 1960. You can find Ella's biography and more information about her personal life and legacy here and here.