JohnKim

You might want to check Magoosh' blog for that: https://magoosh.com/gre/2016/gre-scores-for-top-universities/

Just saw this post on Quora:
IELTS (International English Language Test System) and TOEFL (Test of English as a Foreign Language)
Both are English Language Tests to determine one’s ability to communicate in English. The major difference of both are as follows
Style of English Exam - IELTS has different question types, ranging from fill in the gap, short answer and essays. TOEFL is more on multiple choices. Developer/Administration Council - TOEFL is administered by Education Testing service, a US-based organization that also handles SAT. On the other hand, IELTS is administered by British Council, University of Cambridge ESOL Examinations and IDP Education Australia. Language - IELTS is more likely British English while TOEFL is more on American English Hope this can answer your question.

Depends completely on each school. You could contact each department that lists this to find out. At my PhD school, programs could only choose between "Required", "Strongly Recommended" or "Not Required". If it's "Not Required" then applicants cannot submit scores. So, programs that want an optional reporting have a website that says "Strongly Recommended" even though it could really just mean "completely optional". However, other places are more like what you've said: they expect you to take it unless you have some other reason, or they expect some people to take it (e.g. a multidisciplinary program related to Physics might expect you to take the Physics GRE if you had a Physics undergrad but not if you are coming from a Biology degree with the intent to do Biophysics research). So if in doubt, just ask!

This is a personal problem I had about a week ago, that I feel like many might be able to relate, and thought they might find useful. 
So you've been studying (or not studying, and think you know it) for the GRE all week (or month), and are ready to take it. You go in, you get jitters, mind farts, hard sections, regardless, things don't go as planned. You get your score, and they're (or its) bad. Not oh I wanted a 163 I got a 160 bad, but moreso: "I wanted a 160 and I got a 148 bad". Now in my scenario, I also had a relatively weak GPA too. So a bunch of things start running through your mind, am I screwed? Am I an idiot? Maybe I'm not ready for a PhD or MA program? Maybe this is evidence higher education programs aren't for me? Maybe I should lower my standards? There goes top schools in the country, here comes State University of Alabama (not bashing on State Universities or Alabama, SU Alabama might actually be a very good school). Point being, crippling depression and grief come upon you as you start to question your future, your capabilities, and your intellect.
I wanted to create this post, as a feels good, life isn't over section. I've done a couple of research the past week, and have come to a few conclusions, that I feel may help people out. 
1) There are many schools that have amazing programs that are outside of the "famous" top schools in the country. Just because you can't go to Harvard or Yale doesn't mean its all over. You might be surprised to find a lot of lesser known schools that are more lenient (at least in regards to the GRE), but still have great programs.  
2) The GRE is not a representation of your academic ability, intellect, or how well you will do in a PhD program. Just because you did bad on the test, does not mean you're an idiot, or you're going to do bad in whatever program you plan to pursue in the future. 
3) You aren't alone. If there is one thing I have learned the week, it's a lot of people don't do amazing their first time. Nor are your feelings for doing bad, I think its safe to say, getting a low score on the GRE brings down everyones self confidence, in themselves, and their application. 
Anyways, I'm sure there are a lot more, but these are the things that helped me the most. I was hoping we could get a feels good thread going, statements to help people feel better or get out of that immediate, " I failed the GRE, I'm a failure" spiral. Hope this helps anyone else taking their GRE in the next couple of weeks/months!

Very good question! I have actually found something in Youtube that goes like Practice Tests: Are They Good Enough?, it was an interview of Ashwini Nene.
Hope this video can help you: 
 

I am planning on taking GRE this Fall 2018. Hopefully I can find really helpful tips from GRE experts here in The Grad Cafe!