3.1 Definitions in this standard are to be regarded as the correct ones for terms found in other ASTM standards of Committee D18. Certain terms may be found in more than one standard issued under the jurisdiction of this committee and many of these terms have been placed in this standard.

3.2 Terms that are defined in some textbooks may differ slightly from those in this terminology standard. Definitions in this terminology standard are to be regarded as correct for ASTM usage.

3.3 See Appendix X1 for References.

3.4 Definitions marked with (ISRM) are included for the convenience of the user and were taken directly from the International Society for Rock Mechanics (see X1.3).

3.5 A number of the definitions include symbols. The symbols appear in italics immediately after the name of the term.

3.5.1 No significance should be placed on the order in which the symbols are presented where two or more are given for an individual term.

3.5.2 The symbols presented are examples; therefore, other symbols are acceptable.

3.5.3 See Appendix X2 for ISRM Symbols.

3.6 A number of definitions indicate the units of measurements in brackets and which follow the symbol(s) if given. The applicable units are indicated by italic capital letters, as follows:
 D-Dimensionless
 F-Force, such as pound-force, ton-force, newton
 L-Length, such as inch, foot, millimeter, and meter4
 M-Mass, such as kilogram, gram
 T-Time, such as second, minute

3.6.1 Positive exponents designate multiples in the numerator. Negative exponents designate multiples in the denominator. Degrees of angle are indicated as "degrees."

3.6.2 Expressing the units either in SI or the inch-pound system has been purposely omitted in order to leave the choice of the system and specific unit to the engineer and the particular application, for example:
 FL⁻²-may be expressed in pounds-force per square inch, kilopascals, tons per square foot, etc.
 LT⁻¹-may be expressed in feet per minute, meters per second, etc.

3.7 Where synonymous terms are cross-referenced, the definition is usually included with the earlier term alphabetically. Where this is not the case, the later term is the more significant.

3.8 Grouping of Definitions and Listing of Related Terms-To aide users in finding terms, this terminology standard provides grouping of definitions and listing of related terms.

3.8.1 Groupings-Some of these groupings of definitions are consolidation, density, head, measurement, unit weight, and specific gravity.

3.8.2 Listings (see Appendix X3)-The listing of related terms might be headed by such items as aquifer, compaction, density, gradation, index, specific gravity, and unit weight.