Facebook lite means it is a lite version of facebook. As facebook app has high usage, therefore the lite version is build for the smaller usage of data.
Facebook Lite is available on Google Play and it is just 435KB in size, runs on Android 2.2 and above, so even if you’re using an older phone, you can probably take advantage of this application.
It works as like as the facebook app( main), but as it is a lite version it consumes less data, this is due to compressed images, compressed videos, etc.
And the main advantage is that, we can also do messaging on facebook lite .
So I highly recomend to use this app, for those who want to save thier consumption of internet data.