What is the meaning of Ap.?

Abbreviation of apud, used in scholarly works to cite a reference at second hand.

abbreviation of a podobně: and so on

abbreviation of aamupäivällä (“before noon, in the morning, ante meridiem”); am, a.m.

abbreviation of après

abbreviation of altpersisch (“Old Persian”)

abbreviation of apartament (“apartment”)

abbreviation of a podobne

Source: wiktionary.org