Also called 'Coherence'. One of the five main demands used to measure the quality of cycling infrastructure (the others are safetydirectness, comfort and attractiveness).

Cohesion refers to the extent to which a bicycle network connects up with origins, and destinations - with all points of departure and of arrival. A cohesive network is one in which people who wish to cycle are only a short distance from cycle routes, and that is easily accessible. The CROW manual recommends that, in urban areas, people should have to travel no more than around 250 metres to reach the bicycle network. 

This essentially means that a bicycle network should form a dense grid, for maximum convenience and comfort.

From 'Cycle Traffic and the Strategic Road Network' -

Cycle networks shall link trip origins and destinations, including public transport access points and shall be continuous and easy to navigate. 

Cohesion also implies that the cycle network, and the elements that make it up (cycleways, low traffic streets, cycle paths, et cetera) should be joined up in a consistent and legible way.