Humidity is a measure of how much water vapour is in the air. Warm air can hold more water vapour than cold air.
The reason you often find 'humid' days uncomfortable, is because the air is near or at its saturation point (Relative humidity 100%) this means that the air can hold no more water vapour, so when you sweat, it cannot evaporate if the air is truely saturated. However in practice you will find it will evaporate, just not as much, which leads to people feeling 'sticky' and uncomfortable because they cannot cool down by the evaporation of sweat.
I couldn't tell you if 79% is particularly bad for Cyprus, but if you take a place like a rainforest the relative humidity rarely falls below 80%, with the high temperatures it wouldn't be too nice.