The phrase is defined in the statute:
http://mgaleg.maryland.gov/webmga/frmStatutesText.aspx?article=gcr§ion=10-619&ext=html&session=2018RS&tab=subject5
§10–619.
(a) (1) In this section the following words have the meanings indicated.
(2) “Dangerous dog” means a dog that:
(i) without provocation has killed or inflicted severe injury on a person; or
(ii) is determined by the appropriate unit of a county or municipal corporation under subsection (c) of this section to be a potentially dangerous dog and, after the determination is made:
1. bites a person;
2. when not on its owner’s real property, kills or inflicts severe injury on a domestic animal; or
3. attacks without provocation.