What is the difference between a SIPO payment, direct debit, and a standing order?

It is a permission to debit your account. You always define a limit, payment frequency, and counter-account for direct debits. 

SIPO is a service provided by Česká pošta (Czech Post). It allows you to combine several regular direct debits into a single payment (e.g. rent, telephone, radio). 

It is intended for regular payments of a specific amount in CZK or foreign currency – at a fixed interval to a single payee.