diff --git a/README.md b/README.md
index 32f6d4e..d60a137 100644
--- a/README.md
+++ b/README.md
@@ -8,39 +8,43 @@ options :
 ```
 
 thread :
-- thread are light-weight-process (LWP) that happens inside a process
+- parts of a process that performs code simultaneously
+- thread are light-weight-process (LWP) that happens inside a process (observe with command `ps -eLf`)
 - a process can be single-threaded or multi-threaded
-- different process have a unique PID with a unique LWP, different thread in the same process have the same PID and a different LWP
+- different process have a different PID and different LWP, different thread in the same process have the same PID and different LWP
 - thread vs process :
   process :
   - process is isolated, it doesn't share memory with any other process
-  - process can have states : new, ready, running, waiting, terminated, suspended
   - process is less efficient in communication, it takes more times to create or terminate or switch
   - process speed is not impacted by speed of other process (untill it reach the limit of cpu)
-  - process are created with fork() and execve() (to duplicate a process in a child process, or replacing an existing process)
   thread :
-  - thread are not isolated
-  - thread can have states : running, ready, blocked
+  - thread are not isolated, they share memory with the other threads
   - thread is more efficient in communication, it takes less times to create or terminate or switch
   - thread can become slow if the process does many concurrent tasks
 - ressources :
   - https://www.baeldung.com/linux/process-vs-thread
 
+mutex :
+- mutual exclusion
+- to prevent a part of the code to be performed simultaneously by threads
+- the section of code wraped by a mutex can be access by only one thread at a time
+- the section starts by unlocking a mutex, and end by locking it
+
 
 external function :
 
-- `memset` : fill memory with a constant byte
-- `printf` : format and print data
-- `malloc` : allocate dynamic memory
-- `free` : free dynamic memory
-- `write` : write to a file descriptor
-- `usleep` : suspend execution for microseconds intervals
-- `gettimeofday` : get time
-- `pthread_create` : create a new thread
-- `pthread_detach` : 
-- `pthread_join`
-- `pthread_mutex_init`
-- `pthread_mutex_destroy`
-- `pthread_mutex_lock`
-- `pthread_mutex_unlock`
+- `memset`      : fill memory with a constant byte
+- `printf`      : format and print data
+- `malloc`      : allocate dynamic memory
+- `free`        : free dynamic memory
+- `write`       : write to a file descriptor
+- `usleep`      : suspend execution for microseconds intervals
+- `gettimeofday`: get time
+- `pthread_create`       : create a new thread
+- `pthread_join`         : wait for a thread to finish, 
+- `pthread_detach`       : when a thread is detached it cannot be join, you cannot wait for it to teminate, it will release its ressources on its own when it has finish
+- `pthread_mutex_init`   : initialize a mutex
+- `pthread_mutex_destroy`: destroy a mutex
+- `pthread_mutex_unlock` : unlock a mutex
+- `pthread_mutex_lock`   : lock a mutex