The common name for an outside tap is a Hose Union Bib Cock. These are subject to all variants of weather and heat and can be troublesome.
Ensure the shaft going into the brass body of the tap is lubricated with a smear of silicone grease, do not use oil-based products. Opening the tap fully, smear the shaft with lubricant and close the tap. This will ensure the top gland seal remains lubricated and will make the tap easier to operate. If water is leaking form the top of the tap, the gland nut can be tightened. Do not overtighten. If the tap is leaking from the spout the easiest way to resolve is to replace the tap completely. This can be achieved by isolating the water supply to the tap either by the isolating valve going to it or turning off the mains stop cock to the property. The tap will unscrew in an anti-clockwise direction, a wrench will be needed. The new replacement tap can be fitted in the same manner and we recommend 10 – 15 turns of PTFE tape is used on the male thread of the tap to make a water-tight seal. Turn the water supply back on.