What is the meaning of Pl.?

Abbreviation of plural.

Abbreviation of plates., often used to indicate the number of plate-based illustrations in a book

Abbreviation of pois lukien (excluding).

e.g. (for example)

Abbreviation of plentas.

Abbreviation of plac (square (in a town)).

Abbreviation of pluralis (plural number).

Source: wiktionary.org