What are some non-CS concepts that can be defined using BNF notation? I'm preparing a class on the modified BNF notation that python uses. I.e.,


  Each rule begins with a name (which is the name defined by the rule) and ::=. A vertical bar (|) is used to separate alternatives; it is the least binding operator in this notation. A star (*) means zero or more repetitions of the preceding item; likewise, a plus (+) means one or more repetitions, and a phrase enclosed in square brackets ([ ]) means zero or one occurrences (in other words, the enclosed phrase is optional). The * and + operators bind as tightly as possible; parentheses are used for grouping. Source 


For this class, I'm not allowed to assume the students have prior knowledge in CS. Thus I must rely on concepts from general knowledge to provide examples in the use of BNF. 

In other words, I can't use something like

longstringitem ::= longstringchar | stringescapeseq,

I must use something like this instead:

digit ::= 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9
"a digit is defined as either 0 or 1 or 2 or 3 or 4 or 5 or 6 or 7 or 8 or 9"

What are some non-CS concepts that can be used to illustrate the * sign (zero or more repetitions of the preceding item,) the + sign (one or more repetitions,) the phrase enclosed in [] (zero or one occurrences) and the () (used for grouping) from the BNF notation?
Going with real-world things which they should be familiar with are best, even if it is completely outside of education. As you have applied the tag for adult education, I'm going to presume it is outside of normal university/college courses.

A bit of creativity and looking around can develop many an idea as long as you get outside the box. The cafeteria might be a good place to look.

entree ::= pizza | hamburger | steak
side_dish ::= corn | coleslaw | fries
beverage ::= coffee | tea | milk | soda
dessert ::= (apple|pumpkin) pie | (peach|cherry) cobbler | ice cream
meal ::= water beverage* entree side_dish+ [dessert]



  The water is mandatory (already on the table perhaps), it's possible to have as many drinks, and refills, as you wish. There is always an entree, one side dish is included, but you may have more. Finally, if you choose, you may have a desert.


If the situation is at a regular educational institution you can experiment with using degree requirement courses, and electives. There's enough there to allow the students to create their own versions as practice as well.