The BME280 Environmental Sensor with Sensor Modules 27mmx20mm RoHS by Waveshare is a temperature, humidity, and pressure sensor used for monitoring environmental conditions, as well as detecting change in these conditions. It provides temperature, humidity, and barometric pressure information which is very important for applications like weather monitoring, pollution tracking, and climate control. The BME280 is highly accurate and has good temperature response, making it suitable for a wide range of applications. It is also very small, only 27mm x 20mm, and RoHS compliant, making it perfect for embedded projects or projects with limited space.