1. Branch of biology that deals with the study of the cell as a complete unit, and the molecular and chemical interactions that occur within a living cell.
2. A scientific discipline that studies cells – their physiological properties, their structure, the organelles they contain, interactions with their environment, their life cycle, division and death. This is done both on a microscopic and molecular level. (Wikipedia.com)
See also cytology.
Word origin: formerly cytology.