Multiple I2C devices can be connected to the same clock and data lines. This means you can have many different sensors and devices all connected to the same couple pins from your development board. The I2C protocol uses a 7-bit address assigned to each device as a way for the development board to talk to a specific device. As a result of using 7-bit addresses the I2C protocol is limited to 127 unique devices connected to one bus (or pair of data and clock lines).