What are "Tiers"

I have been seeing this tier thing on past topics regarding tuning here in gameplays and discussions . Would anyone briefly explain what is the meaning of it?

power ratings
S, A, B, C

saying something is "S tier" or S+ tier" means it's one of the best things in the game.
A tier would be strong things, but they aren't the best(since they aren't S tier)
B tier would be around around average to below average, things that are usable but not that good, or things that are only good in certain situations.
C tier things are bad and just don't perform well.

Winty wrote:

saying something is "S tier" or S+ tier" means it's one of the best things in the game.
A tier would be strong things, but they aren't the best(since they aren't S tier)
B tier would be around around average to below average, things that are usable but not that good, or things that are only good in certain situations.
C tier things are bad and just don't perform well.

This sounds about right. Here's an example, in terms of ARTs (in my opinion, at least; if anyone wants to correct me or add to the list, feel free to do so)
S: Lily Rain EVE, Mialy
A: Rouche, Fia, Monica, Kagura, Albatreos
B: Lily Rain, Destructor, Victory series, Amateus
C: Cannonballer, Build Arm, Sturbanger

......What bout color tiers tune wise i've been told orange and red by a clanny and i am like... WHAT??

those are likely to be boostrun tier

check the boostrun section of the guide here
http://www.cosmicbreakfanforum.com/t13442-stat-movement-cart-breakpoints

Can someone tell me what is the ranking of colors from highest to lowest?

Tune-wise, blue tunes alter your robot's basic stats (dem gamma tunes actually lower your overall stats...*shivers*). Red tunes (weapon tunes) change the performance of their respective tuned weapons. Yellow tunes (ex-tunes) are the same as most basic blue tunes, except they also improve your bot's HP with no extra cost to yoyr robot's capacity (but getting the materials for them...ugh...)

As for boost run color tiers, I used the chart from http://www.cosmicbreakfanforum.com/t7429-boost-run-short-boost-etc-etc-charts

Highest to lowest: pink, red, orange, yellow, green, blue, indigo, violet, gray, brown, tan...

Lots of people aim for yellow-tier boost run, since almost all non-boost running characters run at green-tier speed at their fastest, and they throw the rest of their points into HP and either STR and/or TEC for more damage. The economy boost run core tune makes this better by making running eat up less boost, but it doesn't have any effect on the tier color (distance = speed * time; tier = speed, eco BR adds extra running time; overall result is that you go farther, but only because you ran for a longer amount of time, not because you got faster).