1. (medicine) Any chemical treatment intended to be therapeutic with respect to a disease state.
2. (oncology, most common usage) chemical treatment to kill or halt the replication and/or spread of cancerous cells in a patient.
Chemotherapy (often abbreviated to chemo and sometimes CTX or CTx) is a category of cancer treatment that uses chemical substances, especially one or more anti-cancer drugs (chemotherapeutic agents) that are given as part of a standardized chemotherapy regimen.
Chemotherapy is a treatment of a disease that consists of one or more chemical compounds. Although it is worthwhile noting that the term, "Chemotherapy" is usually only ever used to describe cytotoxic treatments for cancer.