From OpenStreetMap Wiki
|cycleway = sidepath|
|Indicates that a cycleway (or footway) attendant to a street.|
|Used on these elements|
|Tools for this tag|
|This article or section contains questioned, contended or controversial information. See the talk page for more information.|
The value sidepath is used to indicate if a cycleway (or footway) is attendant to a street.
There are two use cases for this value.
On the main road
On a sidepath
Note that the suffix :right/left/both is not being used in this case.