From: Recurrent discussions

The exact meaning of the term `thread' is not generally agreed upon.
One of the more common usages denotes a `lightweight' process
(sequential flow of control) which shares an address space and some
other resources with others, and for which context switching time is
lower than for `heavyweight' (i.e. kernel-supported) processes.

Throughout the following material, when we refer to `processes', this
can be taken as meaning heavyweight processes.