Define is something that is not in TWIG. A define is similiar to a preprocessor
#define in C, the value gets substituted into the expression.
Subsitution is only within template brackets. Substitution is done during the
compilation of the template. 

{% define PC = [self stringByReplacingOccurrencesOfString:@"S04"
                                               withString:@"***"] %}
{% filter PC %}
  VfL vs. S04 = 4:0
{% endfilter %}