Hello

 -pnum  or  --strip=num

Strip the smallest prefix containing num leading slashes  from  each file  name found in the patch file.  A sequence of one or more adjacent slashes is counted as a single slash.  This controls  how  file names  found  in  the  patch file are treated, in case you keep your files in a different directory than the  person  who  sent  out  the patch.  

For example, supposing the file name in the patch file was

/u/howard/src/blurfl/blurfl.c

setting 

-p0 gives the entire file name unmodified, 

-p1 gives u/howard/src/blurfl/blurfl.c without the leading slash, 

-p4 gives blurfl/blurfl.c

and  not specifying -p at all just gives you blurfl.c.  Whatever you end up with is looked for either in the current  directory, or the directory specified by the -d option.