The X Window System, and thus Cygwin/X, uses its own internal clipboard system that is distinct from the clipboard system used by Windows. Copying and pasting text between these two clipboard systems requires a clipboard integration program that watches for updates to either clipboard and copies data between them when either one is updated.
Cygwin/X has an internal clipboard integration system that is
enabled by default.
See the Section called Command line parameters in Chapter 3
for more information on the -[no]clipboard
command-line parameters.