docs: fix typo (#2563)

Looks like the author intended to write "OS Process"

docs/gitbook/guide/parallelism-and-concurrency.md

@@ -26,7 +26,7 @@ BullMQ allows you to set a concurrency setting on your workers. This setting is
 
 Threads are a mechanism used by the operating system to provide concurrent (and parallel) execution,  by pre-empting a given thread by another one (in the case of threads running in the same CPU), or by running threads in parallel if there are several CPU cores available. In practice however, a modern OS runs hundreds if not thousands of threads at any given time, so actually no guarantee running code in several threads will indeed run in parallel, there is just a chance they will, and this depends a lot on how the given OS has implemented its scheduler, this can be quite complex but as a rule of thumb we can say that if there are 2 threads that consume a lot of CPU, and there are at least 2 cores, then most likely these two threads will run each on its dedicated CPU.
 
-NodeJS has thread support, but it is important to note that these threads are pretty heavy and almost consume the same amount of memory as if they were running in two different SO processes. The reason for this is that every NodeJS thread requires a complete V8 VM, with a lot of built-in libraries, which will add up to several dozens of megabytes.
+NodeJS has thread support, but it is important to note that these threads are pretty heavy and almost consume the same amount of memory as if they were running in two different OS processes. The reason for this is that every NodeJS thread requires a complete V8 VM, with a lot of built-in libraries, which will add up to several dozens of megabytes.
 
 ## How to best use BullMQ's concurrency then?