Missing links is a term that describes gaps in the cycling network, and those gaps can be quite short. An example would be a 100 m of missing path that would connect two good bike paths. Without this short link, a cyclist may need to ride a great distance.
Filling the gap and building a cycling path to form a network does not need to be expensive and it is very worthwhile. The value of fixing the missing link far exceeds the construction costs as it makes the whole path network more attractive to cyclists.