High-pass filter in Python (Scipy)
Filters generally can't just have a single cut-off frequency (otherwise their complexity will be huge).  So a transition region is usually needed. 

In this case, the filter_stop_freq is that frequency below which the filter MUST act like a stop filter and filter_pass_freq is that frequency above which the filter MUST act like a pass filter.

The frequencies between filter_stop_freq and filter_pass_freq are the transition region or band.

Because this is designing an FIR filter, filter_order is just the length (number of taps) of the filter. The higher the order, usually, the better the fit (and the smaller the transition region can be).