The NodeMCU is an open-source IoT development kit that allows users to prototype IoT products using a few lines of Lua script. It contains an ESP8266 WiFi SoC, programmable GPIO pins, 32KB RAM, 80KB DRAM, and 200KB flash memory. The NodeMCU can be programmed via C or Lua and connect to devices via WiFi or by connecting pins to sensors and actuators. It provides a low-cost way to build an interactive and programmable smart device with WiFi connectivity.