|leisure = common|
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Common land (a common) is land which has an owner, but over which other people have certain rights. Historically these rights typically included the right to graze livestock, collect firewood, or cut turf. Today they include the rights to use the land for certain leisure activities.
In the UK common land is registered. The rights to use it typically include leisure activities such as walking or running, sightseeing, bird watching, picnicking or climbing. Rights would normally not include camping, lighting a fire, or holding an event without the owner's permission. The UK government published a register of common land in 2012, which is archived here - 
Use leisure=common to identify land over which the public has general rights of use for certain leisure activities. More specific tags can be added to provide greater precision.
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