The difference here lies in the time at which the termination takes effect. Ordinary termination means that your employment relationship only ends at the end of the notice period. Extraordinary termination, also known as termination without notice, takes effect immediately.
There are also differences with regard to a necessary reason for termination. Termination without notice is only justified if the employer cannot reasonably be expected to maintain the employment relationship until the end of the ordinary notice period, taking into account the interests of both parties.