What is the meaning of 半濁点?

a diacritical mark, such as ゜ on ぱ, used to:

1. derive the kana for a mora onsetted with /p/ from the kana for a mora onsetted with /h/
2. orthographically phonetically denote [ŋ], a realization of /ɡ/ especially occurring word-medially, instead of the standard dakuten ゛, chiefly in pronunciation dictionaries

derive the kana for a mora onsetted with /p/ from the kana for a mora onsetted with /h/

orthographically phonetically denote [ŋ], a realization of /ɡ/ especially occurring word-medially, instead of the standard dakuten ゛, chiefly in pronunciation dictionaries

Source: wiktionary.org