(Or "linear analysis", "scanning") The first
stage of processing a language. The stream of characters
making up the source program or other input is read one at a
time and grouped into lexemes (or "tokens") - word-like
pieces such as keywords, identifiers, literals and
punctutation. The lexemes are then passed to the
parser.
["Compilers - Principles, Techniques and Tools", by Alfred
V. Aho, Ravi Sethi and Jeffrey D. Ullman, pp. 4-5]