A checkpoint in the cell cycle is a regulatory mechanism that ensures the proper progression of the cycle and the fidelity of cellular division. These checkpoints monitor critical events such as DNA replication and the integrity of the genetic material, assessing whether a cell is ready to proceed to the next phase. If issues are detected, the cell may be halted, repaired, or directed to undergo apoptosis, preventing the propagation of damaged cells and safeguarding against diseases like cancer.