1. railroad track having the standard width of 56.5 inches;
The Collaborative International Dictionary of English v.0.48:
Standard \Stand"ard\, a.
1. Being, affording, or according with, a standard for
comparison and judgment; as, standard time; standard
weights and measures; a standard authority as to nautical
terms; standard gold or silver.
2. Hence: Having a recognized and permanent value; as,
standard works in history; standard authors.
(a) Not supported by, or fastened to, a wall; as, standard
(b) Not of the dwarf kind; as, a standard pear tree.
Standard candle, Standard gauge. See under Candle, and
Standard solution. (Chem.) See Standardized solution,
WordNet (r) 3.0 (2006):
n 1: railroad track having the standard width of 56.5 inches