Is there a good online dictionary/encyclopedia for mathematics? I'm an engineer/physicist by training, and typically, my publications are in journals where the readers do have an semi-advanced understanding of math, but not at a serious mathematician's level. So often, when I use some transform or a function that is not known to the community, I'd like to point them to a reference that's precise, yet simple to read and readily accessible. It seems unfair to point them towards a dense article/book that might be the best in the field, yet completely useless to someone reading my paper.
What I'm looking for, would be an online form of the Encyclopedic Dictionary of Mathematics (EDM), which is a remarkable reference. This is my favourite option, but I'd like to know if there are online alternatives (by a trusted body, not a run of the mill math-o-pedias that float around), which makes access easier. 
One that comes to mind is Wolfram MathWorld (WM), which although impressive, can be lacking at times (to put it this way, they have very good references on mathematical concepts that Mathematica is capable of doing). The Digital Library of Mathematical Functions (DLMF) is not bad either, but doesn't come close to the EDM. 
Lastly, Wikipedia (WP) is pretty decent, especially in conveying concepts to the lay reader. However the anyone-can-edit it feature makes it a little less reliable than the other three.
For now, my feeling is that EDM $\gt$ WM $\approx$ DLMF $\geq$ WP. Do you have suggestions? 
If you think otherwise of my rating of the references, please do let me know why... perhaps I might have overlooked a few aspects in evaluating them and am open to reviewing them. 
 A: Other than wikipedia,  there's wolfram's site http://mathworld.wolfram.com/
and there's also a free collaborative encyclopedia at http://planetmath.org/
A: www.wikipedia.org is the most comprehensive online mathematics resource I have found.  It is also extremely reliable, although at times a little opaque.  
A: http://encyclopedia-of-equation.webnode.jp/ is a nice website of mathematical identity equation.
A: If you're talking about Laplace transforms or other things then I wouldn't know of texts that have simple explanations to what they mean, in fact only by going through the mess of doing it can one understand even a bit of what's being said. So ultimately it depends on how much your readers do want to understand.
Since you're an engineer/physicist by training, you deal with a lot of differential equations so I suggest Morris and Tenenbaum's Ordinary Differential Equations, it's a great book and furthermore it's for students of science and engineering, I use it for my differential equations class.
In fact the chapter on Laplace Transforms is not hard at all, great for a quick reference. 
But if you're invoking stuff from complex analysis then 100% I would suggest Needham's Visual Complex Analyis, it's not even that complicated and it's full of pictures that illustrate beautifully what's happening!
Good luck in finding what you need,
Ben
A: The Princeton companion to mathematics is also available online if you have an Ebrary subscription.
