It can mean fornication, prostitution, adultery, etc. Jesus is possibly saying that divorce is permissible if sexual immorality is committed.
Maaari itong mangahulugan ng pakikiapid, prostitusyon at iba pa. Posibleng sinasabi ni Hesus na pinapayagan ang diborsyo kung may naganap na sekswal na imoralidad sa pagitan ng magasawa.