Final answer:
Undocumented immigration refers to individuals without legal status in the US. In 2015, there were approximately 11 million undocumented immigrants. The pattern of undocumented immigration has fluctuated since the peak year.
Step-by-step explanation:
Undocumented immigration refers to individuals who do not have legal status to live or work in the United States. As of 2015, it was estimated that there were approximately 11 million undocumented immigrants in the US. The peak year for undocumented immigration is not specified in the provided information, but since then, there has been a pattern of fluctuation in the undocumented immigrant population.