Ah - it's embedded text data saved inside a jpg which can include when a picture was taken, the camera model, the aperture setting, shutter speed, even down to its location if the camera has a GPS receiver.
I can't direct you on how to see this data on Windows since I use Linux which will be different, but I would image there will be a facility in your image viewer to view 'properties' or some such which will list all the meta data that was captured when the picture was taken.
It can be very useful - but not for images saved from AW since they strip all the meta data out of uploaded pictures. But if a girl sends you some face pictures for example, then it's always good to have a sneaky look at the meta data just in case there's something interesting there - like the date the photo was taken. If it's years ago, then you have some warning things may not be all they seem with the girl in question.