Sorry it is a noobish question but people keep mencioning them and I have no idea what they mean so I was hopping someone could tell me by asking, thanks.
This are smogon tiers.
Please have a look at the answer to this wquestion. It should explain everything you need.
Lazy Chance Breaker FTW!!
They are tiers! Overused, Never Used, Underused, Little Cup are the first four. Ubers consists of mostly legendary Pokemon, and also includes really strong non-legendary Pokemon, mostly because of abilities. I hope this helps! -Jellohamster
They're all tiers which are used to categorize Pokemon by the strength.
Since Blob's answer is better here it is.