The ESP8266 ESP-07 module is a Wi-Fi module that allows microcontrollers (like Arduino) to access a Wi-Fi network. The ESP-07 is the SMT (surface mounted technology) version of the ESP8266 Wifi module. This is good if you need compact and low-profile designs.
This module is a self-contained SOC (System On a Chip) that doesn’t necessarily need a microcontroller (but you still can) to manipulate inputs and outputs as you would normally do with an Arduino, for example, because the ESP-01 acts as a small computer.
Depending on the version of the ESP8266, it is possible to have up to 9 GPIOs (General Purpose Input Output). Then, we can give a microcontroller internet access like the Wi-Fi shield does to the Arduino, or we can simply program the ESP8266 to not only have access to a Wi-Fi network, but to act as a microcontroller as well. This makes the ESP8266 very versatile, and it can save you on cost and space in your projects.
1*Serial Port Wireless Module