What is Consider a Good Chess Rating on this Site?

A good rating=Your current rating+100 pts.

That is infinitely true

If you think that your rating is good, then it is

Some people are grateful for what they have. Some always aspire for what they don't have. Guess which group are happier.

Is 271 decent for someone who has been playing chess for 4 days

not really, but it's good that you've started and are looking to improve. Doing puzzles may help you get better and learn tactics, overall with time you'll get better

271 is about average. If you are calling good not terrible, then yes that is good.

800 to 900 is average being in the 50th percentile

Falling below 1850 in rapid yet again this morning, I feel that my game is rubbish.

Less than 1000 begginer, 1000-1999 average, 2000+ advanced

I think most people will answer like this: Whatever rating doesn't stand a chance against me personally is bad, just below my current rating is starting to be good, just above my current rating is good to quite good. 2000-ish players see it differently - they tend to think of where someone is at on the journey to where they are at, so 1200 is still a beginner from the point of view of one of the lucky few that ever reach 2000. But they are also comparing everyone else to where they currently stand, just adding a time dimension, if you will. If you want to be objective about it, go to your stats page, and pay attention to your percentile ranking, and the number of players. The larger the number of players (like rapid) the more representative a sample you have of all players across the site, the smaller the number of players (like bullet), the less representative it is (because not everybody can handle bullet time controls, it doesn't get as many players).
Once you know your percentile, ask yourself, if this wasn't chess, what would I consider "good"? It is a relative term after all. If you think of an above average runner as "good", then if your rapid percentile is over 50%, consider yourself "good". If you would only think of the top 10% of runners as "good" then, you need to be over the 90th percentile. And you need to lighten up. But big picture wise, I say just enjoy the journey. Judge yourself by your progress more than your rating. So long as you are improving, you are on your way.

FIDE rating system applies for only FIDE.

If you are not FIDE, then your rating here is compared against this site. 1000 lands you in the top 20 percent. That means you are good, well above average.

LOL, sounds like you believe humility is not a common virtue
Tbf I did see that once, a person posting their opinions of diff ratings, and put their own rating category as the first one that was "quite good" XDDD
I think that after @Deadmanparty raised the point of the issue of the inappropriateness of applying FIDE standards in all situations, I have now two standards in my head -- one more oriented towards the general population, and another which I measure myself by to goad myself forward, that aligns pretty well with the FIDE standard I think.
However, the claim that 271 is average is simply wrong. I just checked and 500 is about 35th percentile, so many of the active players here have learned the basics and are starting to grasp some things about chess.

Good

I'm at the level of 900 or just below that right now.

When I used to play games on chess.com without an account playing as a guest I found that if I picked the beginer option my games were too easy, intermediate was just about right. I'd probably be thrashed if I picked anything above intermediate.

My level on blitz games is something like 200, after taking a long break from chess I just don't have much instinctive knowledge about the game. I need to sit down and think about my moves slowly.

Good, shmood. I'm just in awe of players who don't hang their Queen.

People who play a couple of games of chess get a rating on this website. It doesn't make sense to me to look at percentages here, comparing yourself to people who play chess more or less regurarily makes much more sense to me. I think 1300 rapid, 1000 blitz is around when people start to make horrible blunders a lot less often, when they can spot basic tactics more or less consistently and when they understand the basics of chess openings and chess principles. 
Here is my ranking of the players (I assume that we are talking about rapid rating on this website):
I would say that below 850 you are a beginner.
850-1299 you are an advanced beginner
1300-1499 lower intermediate
1500-1799 intermediate
1800-2199 upper intermediate
2200+ advanced
somewhere around 2300-2400 good at chess.
For the record, as of the moment of writing this comment I am rated 2016 rapid, 1809 blitz on this website.

Anish Giri recently said that when he was 2100, he “was already quite good”.

I would have to disagree, because 1300 would put you in the top 10%, which seems to be better than "lower intermediate".

How about - 1500+ Strong player

1200 - 1500 Competent

900 - 1200 Novice

600 - 900 Beginner

Under 600 Muppet

This would be for rapid as faster stuff isn't really chess.

On this site, lower intermediate are at the 95th percentile.

@dude0812 - I may be wrong, but I do believe that the percentile ratings only include players who have played a rated game under that time control w/in the last 90 days. I've seen friends go inactive for a while, and their percentile disappears to an "N/A". I've also got lots of people on my friends list that have been playing for 5+ years, have 5K-20K games on the site, are now improving rating wise at maybe 10-20 points a year if at all... And yet according to your ranges, they are "beginners". From my own experience, when I was around the range you say people are just able to spot basic tactics and have just started to learn opening principles, I had read books by Pandolfini, Silman, Chernev, Nimzo, I could have named the opening being played though not the variation, I could and did set up a windmill or smothered mate in a live game, solve about 80% of Polgars 5334 mate in 2s given enough time and 50% immediately. I'm not saying what you have said is untrue, just that it is based on your experience. It is true for players who will one day reach the 2000s - you folks could reach 1000 without studying opening principles, and the rest of us salute you for it. But if you are somebody who is going to max out at 1700, 1500, etc, then you didn't break 1000 during the beginning phase of chess life.