Used to express that something is relatable. Similar to 'Same,' but 'Mood' became more common around 2016.
If something is especially relatable, one might say 'Big Mood.' This implies that your whole being is one and the same with whatever you are commenting on.
(commenting on a photo of a cat who looks super lazy) Mood af
2017 mood = self care and positive visualization
(caption on photoset of Keanu Reeves
looking mad existential) big mood