• What is
    • a patch
      A patch is a piece of code written in some computing language that when added to a main program it enables the original program to do actions that was unable before (or viceversa). For example Alpine does not send e-mail from the command line without pressing ^X. A patch can make Alpine do this, so it can be used from a script.
       
    • a Hunk
      Every patch is composed of a finite number of Hunks. Every hunk contains the necessary information to patch a file. This information includes the old code as well as the new code. For most patches in this web page, hunks are separated by the string *************** at the beginning of a line. For example:

       
      ***************
      *** 139,144 ****
      --- 139,149 ----
             pico_all_done = 0;
             km_popped = 0;
       
      +      if (pm->auto_cmds){
      + #define CTRL_X 24
      +      if ((pm->auto_cmds[0] == CTRL_X) && (pm->auto_cmds[1] == 'y')){
      +         return (1);}}
      +        if(!vtinit())     /* Init Displays. */
            return(COMP_CANCEL);
       
       
      is a Hunk. When a patch is being applied 1 or more hunks are being applied to the same file.
       

      See also:
      How do I apply a patch?
      How do I read a patch?
      How do I know if the patch was applied correctly?
       

    • a diff file
      A diff file is the file that contains the patch. Its name comes from the fact that these kind of files is created by recording what the added code to a program is by comparing it with the original, this means that it records the differences between two files.
       
    • to apply a patch

      To apply a patch is the process of adding the extra code to the "clean" program. You get a new program, which after compiled should have the new feature that you are expecting to get for applying the patch.
       

      See also How do I apply a patch?
       

    • to reverse a patch
      Reversing a patch is your ability to return to the original code without the patch, which means a make believe that nothing ever happened to the program, no code was ever changed.
       

      See also How do I reverse a patch?