It usually means a language that is "block structured", having blocks of code that are treated as a unit for purposes of if/then/else. Blocks are delimited by things like BEGIN/END, DO/DONE, IF/ELSIF/ENDIF, IF/FI, or now commonly curly braces { your; code; here; }. Prior to this, IF's tended to be plain:
IF GOTO A
Where label A can above or below, anywhere in the translation unit, and that was all there is to the IF.
There was also the more notorious Fortran "computed goto" (from memory):
IF A, B, C
Where A, B and C are labels where ever they may be corresponding to a negative, zero, or positive evaluation result of the expression.
"Structured" languages are characterized by not (usually) needing labels for if operations and loops. Now you can guess C is considered structured language because of the fact that it does not force/require goto (labels) statement for the loops or conditional operation.
