Unconscious biases are social stereotypes about certain groups of people that individuals form outside their own conscious awareness. Everyone holds unconscious beliefs about various social and identity groups, and these biases stem from one’s tendency to organize social worlds by categorizing.
Unconscious bias is far more prevalent than conscious prejudice and often incompatible with one’s conscious values. Certain scenarios can activate unconscious attitudes and beliefs. For example, biases may be more prevalent when multi-tasking or working under time pressure.

Staats, C. (2013). State of the science implicit bias review (PDF). Retrieved from http://kirwaninstitute.osu.edu/docs/SOTS-Implicit_Bias.pdf.Unconscious bias.