MEMS mics can detect sound and convert it to voltage, but they're way smaller and thinner. This microphone doesn't even have analog out, its purely digital. The I2S is a small, low cost MEMS mic with a range of about 50Hz - 15KHz, good for just about all general audio recording/detection.
Instead of an analog output, there are three digital pins: Clock, Data and Left-Right (Word Select) Clock. When connected to your microcontroller/computer, the 'I2S Master' will drive the clock and word-select pins at a high frequency and read out the data from the microphone.
More information is available on the website of Adafruit.