also leading,the sharp end

Climbing term, used when the climber starts from the ground up, placing running protection or runners along the way. Trad climbing uses placed natural protection while Sport climbing uses fixed bolts to achieve the runners.

In the event of a fall the climber will only fall twice as far as the distance between their last runner and their harness

The risk is that the protection may fail or the climber may not be able place a piece of protection in sufficient distance to prevent either a screamer (sometimes bad) or a ground fall (always bad)

Climbs on which either there are fewer bolts than a climber might desire (this is a often a subjective judgment) or in which runners cannot be placed due to a lack of weaknesses in the rock are said to be run out.
Some grading systems signify this with a R or an X after the technical grade for the climb. R meaning run out. X meaning significant danger to the climber should they fall (protection failure is likely)

Often a lack of protection adds excitement to a climb. Again it depends on the ability and head space of the person climbing