What is the difference between 7.1 and 5.1 audio for blu rays?

[Movie shy]

Hi everyone,

I do not have a surround sound system my speakers are just in my HD tv. I am trying to figure out the difference in all the audio that comes on a Blu Ray. I know there is 7.1 Lossless and 5.1 and others. If someone could explain the differences it would be greatly appreciated. I was under the impression that most Blu Ray's would automatically default to the best sound possible but that's not always the case and you need to go into the set up to change Audio on some blu ray's. My tv is on the smaller side and as I said I have no surround system. I am not sure what the best audio would even be for myself to play on a blu ray disk. Thanks.