What is the difference between metabolism and catabolism?

Catabolism is one arm of metabolism.  The other arm is anabolism.

Metabolism is a term for the overall energy economy of a cell or organism.  It has two components: catabolism and anabolism.  Catabolism is a term for the generation of usable energy in the form of ATP from the breakdown of energy-yielding substrates (fuels, e.g. carbs, protein, fat).  Anabolism, on the other hand, takes that ATP that is generated from catabolism to do the work of making new new stuff for either growth or maintanence--new proteins, nucleic acids, cells, etc.

Metabolism is usually divided into two categories. Catabolism breaks down organic matter, for example to harvest energy in cellular respiration. Anabolism uses energy to construct components of cells such as proteins and nucleic acids.