Shocking is like letting a manoeuvre slowly slip away that allows the sails to be adjusted (the sheets). "Shock the jib" comes back to leave a little slack in the jib sheet. When you shock, you give slack. Be careful not to confuse it with"dump" which means that you release all the tension at once. In marine dropping corresponds to dropping.
The opposite of"shock" is"tuck in". A sail is trimmed by taking up the tension of the sheet. Thus"jib trim" is like pulling - often with the help of a winch - on the jib sheet.
Careful, you don't tuck in a halyard! Indeed, this manoeuvre is used to hoist the sail (and not to adjust it). To tension the sail upwards, we then talk about tensioning a halyard..
