"...an ordinary statement"

Ordinary in the sense of simple - in contrast to compound statements. This is less ore more described in the Camel Book Chapter 4. Statements and Declarations.

From 4.1 Simple Statements: A simple statement is an expression evaluated for its side effects. Every simple statement must end in a semicolon, unless it is the final statement in a block. In that case, the semicolon is optional--Perl knows that you must be done with the statement, since you've finished the block. But put the semicolon in anyway if it's at the end of a multiline block, because you might eventually add another line.

From 4.2. Compound Statements: A sequence of statements within a scope is called a block...Compound statements are built out of expressions and BLOCKs. Expressions are built out of terms and operators. In our syntax descriptions, we'll use the word EXPR to indicate a place where you can use any scalar expression. To indicate an expression evaluated in list context, we'll say LIST....

Please see ibidem for more details. Still a good read.

Best regards, Karl