Software propagation is a general term for the copying & duplication of software, and was explicitly defined in version 3 of the GNU General Public License. The term is deliberately intended to distinguish between the activities permitted by free software licenses and those that are forbidden by various systems of copyright.
Defined by GNU GPL v3
To "propagate" a work means to do anything with it that, without permission, would make you directly or secondarily liable for infringement under applicable copyright law, except executing it on a computer or modifying a private copy. Propagation includes copying, distribution (with or without modification), making available to the public, and in some countries other activities as well.
References
Software propagation Wikipedia(Text) CC BY-SA