Awesome
Understanding Mathematics 
Articles
- Understanding Mathematics, a study guide by Peter Alfeld
- How to Develop a Mindset for Math at BetterExplained
- Understanding Math Concepts at AllKindsOfMinds
- What is conceptual understanding? by Keith Devlin
- Learning to Learn: Math Abstraction at BetterExplained
- How to study math by Paul
Papers
- Teaching Mathematics for Understanding by Van De Walle
- Can We Make Mathematics Intelligible? (1981) by R. P. Boas
- A Mathematician's Lament by Paul Lockhart
- How to Survive Your College Math Class (and Take Home Something of Value) by Matthew Saltzman and Marie Coffin
- Mathematics, morally by Eugenia Cheng
Books
- How to Solve It: A New Aspect of Mathematical Method by George Polya
- Measurement by Paul Lockhart
- A Mathematician's Lament by Paul Lockhart
- The Art and Craft of Problem Solving by Paul Zeitz
Videos
- Mathematics - The Language of the Universe
- The World of Mathematical Reality by Paul Lockhart
- Paul Lockhart teaching Go by Chaelim "Addy" Kim
- Five Principles of Extraordinary Math Teaching TEDx talk by Dan Finkel
Online Questions
- How to study math to really understand it and have a healthy lifestyle with free time? at Math StackExchange
- How do math geniuses understand extremely hard math concepts so quickly? at Quora
Slides
- Teaching for Conceptual Understanding: Exciting Mathematics by Juanita Copley
Mathematical Language
Links to resources talking about "the mathematical language" and how to overcome problems encountered when reading, writing, interpreting and listening to mathematics.
Articles
- Language of mathematics at Wikipedia
- Mathematical Words: Origins and Sources by John Aldrich
- Communicating in the Language of Mathematics by David Moursund and edited by Dick Ricketts
- How to write mathematics clearly and keep more readers by Matthew Leitch
- How to understand math formulas at Interactive Mathematics
- The symbolic language of math by Charles Wells
Papers
- The Language and Grammar of Mathematics
- Reading Mathematics by John Hamal Hubbard
- A Guide to Writing Mathematics by Dr. Kevin P. Lee
- Mathematics and the Language of Nature by F. David Peat
- The language and grammar of mathematics by Timothy Gowers
- Learning the Language of Mathematics by Robert E. Jamison
Books
- Handbook for Spoken Mathematics by Lawrence A. Chang, Ph.D. (with assistance from Carol M. White and Lila Abrahamson)
- A Handbook of Mathematical Discourse by Charles Wells
Videos
- Math isn't hard, it's a language TEDx talk by Randy Palisoc
Mathematical Notation & Terminology
Articles
- List of mathematical symbols at Wikipedia
- Mathematical operators and symbols in Unicode at Wikipedia
- History of mathematical notation at Wikipedia
- Mathematical and scientific symbols at http://www.uefap.com/
- LaTeX Math Symbols prepared by L. Kocbach (on the basis of another document by David Carlisle, Manchester University)
- Mathematical notation at Wikipedia
- Set notation at Wikipedia
- Notation in probability and statistics at Wikipedia
- Notation for differentiation at Wikipedia
- List of mathematical symbols by subject at Wikipedia
- Statistics synonyms at Wikipedia
- Glossary of probability and statistics at Wikipedia
- Glossary of calculus at Wikipedia
- Glossary of set theory at Wikipedia
- Glossary of linear algebra at Wikipedia
- Glossary of graph theory at Wikipedia
- Glossary of game theory at Wikipedia
- Glossary of mathematical symbols at Wikipedia
- List of mathematical constants at Wikipedia
- Glossaries of mathematics (it also includes other glossaries for more advanced topics) at Wikipedia
- LaTeX/Mathematics at Wikipedia
Papers
- Mathematical Operators at http://unicode.org
- Some Common Mathematical Symbols and Abbreviations (with History) by Isaiah Lankham, Bruno Nachtergaele, Anne Schilling
Books
- Mathematical Notation: A Guide for Engineers and Scientists by Edward R. Scheinerman
- The Cambridge Dictionary of Statistics by B. S. Everitt and Anders Skrondal
Videos
- Mathematical Notation - The Language of Mathematics by Sarada Herke
Slides
- Maths in Lectures: Understanding the Notation by Dr. David Butler
Online Questions
- All questions about mathematical notation sorted in descending order of votes at Math StackExchange
- All questions about mathematical notation sorted in descending order of votes at Stack Overflow
- All questions about mathematical terminology sorted in descending order of votes at Math StackExchange
- Where can I learn about mathematical notation? at Math StackExchange
- How to learn mathematical notation? at Stack Overflow
- How to become comfortable with mathematical notation? at Ask MetaFilter
- What is the status of generating LaTeX from handwriting at Tex StackExchange
Websites
Github
- math-as-code by Jam3 (Github's repository)