diff --git a/README.md b/README.md
index 471e33e..3891cc0 100644
--- a/README.md
+++ b/README.md
@@ -9,6 +9,10 @@ This repository contains the implementation of a USB command handler for the Zep
 3. **usb.c/h**: Manages USB initialization, data reception via UART, and sending responses. Includes a USB thread.
 4. **usb_conf.c/h**: Configures the USB device.
 
+### ACK
+
+Every command returns either an ACK or NACK.
+
 ### Command Structure
 
 ```c