Cremation is a method used to dispose of the remains of a deceased person, and involves burning the body of a deceased person. It is an alternative to other forms of disposition, such as burial.
In his will, Captain James T. Kirk stipulated that he preferred that his body was cremated following his death and not buried in space as was popular among Starfleet officers. (TOS novel: The Entropy Effect)
Following Zarabeth's death, Zar preferred that his mother's body was cremated, but he was not able to obtain any firewood to do so. Spock later performed the cremation using a hand phaser. (TOS - The Yesterday Saga novel: Yesterday's Son)
Among some Cardassians tradition called for the deceased to be cremated. Prylar Obanak Keelen told Captain Benjamin Sisko that he would perform the necessary rights for the dead Cardassian bodies in order for them to enter the Divine Labyrinth. (DS9 - Millennium novel: The Fall of Terok Nor). Other Cadassians opted for burial instead of cremation. (DS9 episode: "Duet")