The word propagation can mean:

• Multiplication or increase, as by natural reproduction.
• In genetics, propagation is another term for the elongation part of transcription.
• In agriculture and horticulture, propagation is the production of increased numbers of plants, by seeds, cuttings, grafting or other methods.
• In religion, propagation is a term often used for winning new converts to the particular religion.
• In physics, propagation is the motion of waves through or along a medium.

Note: For electromagnetic waves, propagation may occur in a vacuum as well as in material media.

Source: from Federal Standard 1037C

See also: photon, waveguide, polarization, antenna theory