- A language is
*regular*if its syntax can be expressed by a single EBNF rule without recursion. - Since there is only one, non-recursive rule all symbols on
the right-hand side must be terminal symbols. The right-hand side
is also called a
*regular expression*. - Regular languages are interesting because they can be recognized
by
*finite state machines*. - Alternatively, a language is regular if its syntax can be described by a number of EBNF rules without recursion.