What is the meaning of ‖?

Used to indicate caesuras.

Used to indicate a major prosodic break, which may be any level of prosodic unit if a single bar marks a metrical foot, or may mark the end of a final prosodic unit if a single bar marks the end of a continuing unit.

Used to indicate an unnaturalised or foreign word.

A pointing mark in Anglican chant, used to mark the place in a verse which corresponds to the double barline in the chant, in circumstances where this is not the same place as the colon which divides the two halves of the verse; typically done when one half is very short.

Used to indicate concatenation.

A footnote indicator; traditionally the fifth (the sequence going *, †, ‡, §, ‖, ❡)

↑ Bringhurst, Robert (2005). The Elements of Typographic Style (ver. 3.1 ed.). Point Roberts, Washington: Hartley and Marks. p. 69. https://readings.design/PDF/the_elements_of_typographic_style.pdf#page=35

Source: wiktionary.org