What are Powerful backlinks?

Any link is powerful if it comes from a page that has a high PR.

You said the PR.Is that a rating from google?

it is not completely true, Google count many factors like:

- root domain and site PR,
- number of external links on site
- position of your link (header, footer, etc.)
- form of the link (image, anchor text, naked url, etc.)
- site relevancy to your niche

and so on...

These terms which makes a backlink powerful:
1.Relevancy:-website on which you are placing link should be inder your site niche.
2.external links should be less so that your link can get max link juice from there.
3.Link Farm:-Don't place your link on link farms.Link farms are those sites which are specially create for link exchange purpose.
4.Position of your link:-Always try to place your link in content.Because All search engines give more importance to contextual links.
I hope you ll use these tactics for your backlinks to make powerful backlinks.
Thanks!

The link that have quality, relevancy and high PR as well... consider as powerful backlinks.

Google gives importance to the links from a site which has clean history, a site with more age factor, and a site whose back links count is above 5k.and the links from this kind of a website are powerful links according to the Google.

wiki defines pagerank quite clearly and comes with illustrations too. just enter the word "pagerank" in their search box ( sorry. iam unable to post link as i only have 5 posts)

You are right Big_Lebowski, Backlink site should be relevant to theme and having high PR

High PR links are good. Homepage links are good. Really, Google just wants diversity and naturality. Make it all look even and natual, don't do 5000 blog comments, then leave it, do 100 at a time, a stick some profile and article submissions in there too, along with some social bookmarking.

Forum posting is generate powerful back links.

Powerful Backlinks are that which have high pr and crawled by Google daily.

It depends on your niche.If the backlink isn't from a relevant niche,even though it is from a high pr google doesn't give that much preference to it.

If you want a powerful backlink then you must get the link from authority site that is relevant to your niche and has a good pr.

There have been a lot of people around here stating that Pagerank is exactly that only for PAGES. They must think that because it is called Pagerank it means pages only. I don't think this is true for a few reasons. Pagerank was invented by Larry PAGE one of the Google founders. I think this explains the word page... maybe it does not really mean PAGE but just his last name.

Most important..

1: Old domain
2: High PR
3: Less OBL

its comes form both quality of site and good pr.

Basic thing is, the more "quality" links points to a link, the more trust and value the pointed links get to eye of search engine. While a query is searched by a searcher, search engine bots crawls over the net to index new pages and take note of changes from already indexed pages.
In these indexing and crawling process, the bot remarks links what to index, and how often. In this process, they also remark a page rank of the websites they have indexed or have crawled, it depends on several terms including quantity of the quality inbound links that a certain web page has.
It is advisable to avoid nofollow links while a search engine campaign in order to achieve more trust and link popularity.

Every inbound link counts as a vote to the pointed link and a powerful link basically means a link that already being remarked as trustworthy to search engine bot. From this perspective, links from authority sites and/or blogroll links - can be counted as powerful links. While getting such links naturally is really tough for new websites, though there are some other alternatives of these links which worth almost same as those.