The following terms are developed and/or defined in this grade level's materials.

ACUTE ANGLE  FORMULA  PROTRACTOR 
ACUTE TRIANGLE  FRACTION  QUADRILATERAL 
ADDITION (FRACTION)  IDENTITY (ADDITION)  RAY 
ANGLE  IDENTITY (MULT.)  RECTANGLE 
AREA  INTERSECTING LINES  RECTANGLE (AREA) 
ASSOCIATIVE (ADD.)  ISOSCELES TRIANGLE  REMAINDER 
CAPACITY  LCM  RHOMBUS 
COMMUTATIVE (ADD.)  LINE  RIGHT ANGLE 
COMPOSITE NUMBER  LINE SEGMENT  RIGHT TRIANGLE 
DECIMAL  MEASUREMENT (ANGLE)  ROUNDING 
DECIMAL NOTATION  METRIC UNITS  SCALENE TRIANGLE 
DEGREE (ANGLE)  MULT. PROPERTIES  SEQUENCE 
DEGREE NOTATION  MULTIPLE  SIMPLEST FORM (FRACTION) 
DENOMINATOR  MULTIPLICATION (WHOLE)  SQUARE 
DISTRIBUTIVE (WHOLE)  NAMING AN ANGLE  SQUARE (AREA) 
DIVISIBILITY  NUMERATOR  SUBTRACTION (DECIMAL) 
DIVISION (WHOLE)  OBTUSE ANGLE  SUBTRACTION (FRACTION) 
DIVISION BY TEN  ORDER OF OPERATIONS  TIME 
DIVISION BY ZERO  PARALLEL LINES  TRAPEZOID 
EQUATION  PARALLELOGRAM  TRIANGLE 
EQUILATERAL TRIANGLE  PERIMETER  UNKNOWN 
EQUIVALENT FRACTIONS  PERPENDICULAR LINES  VARIABLE 
ESTIMATING PRODUCTS  PLACE VALUE  VERTEX (ANGLE) 
ESTIMATING QUOTIENTS  POINT  WEIGHT 
EXPANDED FORM  PRIME NUMBER  
FACTOR (WHOLE)  PROBLEM SOLVING  
  
  
  
  
  
The following terms appear in this grade level's materials. At this grade level the terms are used in the lesson proper in examples or illustrations.
The purpose here is to reinforce understanding of the terms.

ADD BY REGROUPING  KILOMETER  ORDERING (NUMBERS) 
ADDITION (DECIMAL)  LIQUID MEASURE  PLACE VALUE (DECIMAL) 
ADDITION (WHOLE)  MEASUREMENT  RENAMING (FRACTION) 
ARRAY (MULT.) (WHOLE)  MEASUREMENT (LENGTH  REPEATED SUBTRACTION 
CENTIMETER  MENTAL ARITHMETIC  RULER 
COLLECTING INFORMATION  MONEY  SYMBOLS FOR ADDITION 
DIVISION WITH DISTRIBUTION  MULT. AND DIVISION  SYMBOLS FOR DIVSION 
DIVISOR, QUOTIENT  MULTIPLES OF TEN  SYMBOLS FOR MULTIPLICATION 
ESTIMATING SUMS  MULTIPLICATION (FRACTION)  SYMBOLS OF GROUPING 
FREQUENCY TABLE  NUMBER LINE (NUMBERS)  TENTHS HUNDREDTHS 
INCH  NUMBER SENTENCE  WHOLE NUMBER 
  
  
  
  
  
A synonym of the following terms are used. The synonym helps to bridge the learner's non mathematical experiences to mathematics terms that will more formally be worked on.
A synonym may also be used because these historical terms may have been replaced by a new vocabulary (k12math.info's list of 1,000 terms has not changed in 40 years).
Wiktionary dictonary may help here.

APPROXIMATION  INEQUALITY (DECIMAL)  PIE APPROACH (FRACTIONS) 
CONGRUENT PARTS (FRACTION)  INEQUALITY (FRACTION)  UNIT AREA 
DIVISION COMBINATIONS  MULT. BY GROUPING  WORD PROBLEM (FRACTION) 
ENGLISH UNITS  PERIMETER (QUADRILATERAL)  WORD PROBLEMS (WHOLE NUMBER) 
  

K12math.info selected the content that appears here. All terms appear in the lesson proper. The selection process is based upon a content analysis of 2013 to advance copies of 2015 student mathematics
textbook series. Series that base their content on 2010 and/or 2012 standards. The analysis also included content that was felt would be needed for the
transistion to CK12 existing textbook series.
Editor's Note: This is a very basic outline of the content and how they are to be developed in the lesson proper. These terms need to be used in examples, illustrations, class activities and homework to help further understand them.
Resources:
Learners age 5 to 11 Grades K through 6 (from Wikieducator's "Come fly with me..." project).
Key points in Writing a textbook. (Especially step 7)
Teaching OER Mathematics.
Learning design a Wikieducator.org project.
Additional observations made while collecting information for this site on unit development in a textbook:
 One type has a chapter unit divided into 3 parts:
Part 1 has a written explanation of the concept being developed (or defined).
Part 2 has examples and illustrations of the concept.
Part 3 classroom and/or homework activities.
 Another approach consists of 2 parts:
Part 1: the concept being developed (or defined) is being used in several carefully designed examples and illustrations.
Part 2: classroom and/or homework activities.
