Trypsinization is the process of cell dissociation using trypsin, a proteolytic enzyme which breaks down proteins, to dissociate adherent cells from the vessel in which they are being cultured.
When the trypsinization process is complete the cells will be in suspension and appear rounded.
For experimental purposes, cells are often cultivated in containers that take the form of plastic flasks or plates.
[1] Serum can be used to inactivate trypsin, as it contains protease inhibitors.
Trypsinization is often used to permit passage of adherent cells to a new container, observation for experimentation, or reduction of the degree of confluency in a culture flask through the removal of a percentage of the cells.