It means splitting the counterclaim into a separate set of proceedings so that it can be decided separately from the divorce application. Here's an example from the Civil Procedure Rules applicable in England and Wales:

Except where these Rules provide otherwise, the court may (...)

(i) direct a separate trial of any issue;
https://www.legislation.gov.uk/uksi/1998/3132/article/3.1/ma...

Contained within the Court’s general powers of management, in Part 3 of the Civil Procedure Rules (“CPR”), is the power to direct a separate trial of any issue (CPR 3.1(i)). Consideration of a split trial features throughout the CPR rules and accompanying practice directions, including CPR Parts 26, 28 and 29.
https://www.kingsleynapley.co.uk/insights/news/clinical-negl...

And here's an explanation from the Romanian Code of Civil Procedure. As it explains, it means splitting a matter into a separate set of proceedings.

Disjungerea cererii reconvenţionale

(1) Cererea reconvenţională se judecă odată cu cererea principală.

(2) Dacă numai cererea principală este în stare de a fi judecată, instanţa poate dispune judecarea separată a cererii reconvenţionale. Cu toate acestea, disjungerea nu poate fi dispusă în cazurile anume prevăzute de lege sau dacă judecarea ambelor cereri se impune pentru soluţionarea unitară a procesului.
https://lege5.ro/gratuit/gyztaojtgy/disjungerea-cererii-reco...