As signal it means, ‘I require a tug’. But when shown by a fishing vessel (which you will recognise by her lights or shapes), it means, ‘I am shooting my nets’. In Morse code the signal is ‘–..’ and in phonetic the word is Zulu.
Trade name of a particular brand of Stern drive.
In navigation, the point in the celestial sphere which is directly above the observer – Le. the extension of a line joining yourself to the centre of the earth.
See PBO rigging.