Cytology is the branch of life science that deals with the study of cells in terms of structure, function and chemistry. Robert Hooke (1635 – 1703) is sometimes seen as the father of cytology.
Based on usage it can refer to:
Cytogenetics
Cytopathology: the study of cellular disease and the use of cellular changes for the diagnosis of disease.
Cell biology, or cytobiology: the study of (normal) cellular anatomy, function and chemistry.