it is very similar to the SAM file format in that you can have "extra information" about the alignment in those key-value pairs. sometimes they are referred to as tags (e.g. in this document "SAM tags" https://samtools.github.io/hts-specs/SAMtags.pdf) the same type of info can be added to PAF.

here is an example of a PAF line

ctgA    45141   0       45141   +       ctgA    50001   0       50001   45141   50001   60      NM:i:4860       ms:i:90254      AS:i:85398      nn:i:0  tp:A:P  cm:i:8494       s1:i:44546      s2:i:0  de:f:0.0000  rl:i:0  cg:Z:28498M4860D16643M

the cg tag is a "CIGAR" string, and various others are just what minimap2 generates by default in the PAF output.