[Eoussama]

EOS stands for End Of String, it's a predefined constant with the value of 0, it's just another way to assign the null terminator, so by doing string[0] = EOS you're theoretically emptying the sting, for more information about how strings operate, read this tutorial: https://sampforum.blast.hk/showthread.php?tid=654471
It's massive, so take your time.