Lexical Analysis

Lexical analysis is the process of taking an input string
of characters (such as the source code of a computer
program) and producing a sequence of symbols called
"lexical tokens", or just "tokens", which may be handled
more easily by a parser.
A token, in computing, is a segment of text, regardess
whether it be readable or comprised of symbols. Tokens
are generally defined abstractly in a context free grammar,
which is fed into a program such as yacc which checks the
stream of tokens for conformity to this grammar.
A parser is a computer program or a component of a program
that analyses the grammatical structure of an input, with
respect to a given formal grammar, a process known as parsing.
In linguistics, grammar is the set of structural rules that govern
the composition of sentences, phrases, and words in any given
natural language.

Related Notes :

Lexical analysis is concerned with scanning the
input for significant clusters of characters called tokens.
The input stream of characters is analyzed using delimiters
and a careful description of the way various types tokens
may be constructed.

Reference/Source :
D. Soda, G. W. Zobrist
February 1989
CSC '89: Proceedings of the 17th conference on ACM Annual Computer Science Conference