adjust wording

threads.tex

@@ -38,7 +38,7 @@
 inherent data sharing if working with threads.}  Note that all threads of the
 same process have equal access to the process virtual address space.
 \item Not all applications are fit for multithreading as some tasks are not
-inherently parallel in nature.
+inherently concurrent in nature.
 \item Even that debuggers typically support threads, debugging changes timing so
 the problem may not reproduce when using the debugger.  That is usually not an
 issue in a single threaded application.