In economics, a good or service is said to be excludable when it is possible to prevent people who have not paid for it from enjoying its benefits, and non-excludable when it is not possible to do so.
Examples
An architecturally-pleasing building, such as Tower Bridge, creates an aesthetic non-excludable good, which can be enjoyed by anyone who happens to look at it. It is difficult to prevent people from gaining this benefit (although people have tried, by forbidding amateurs from taking photographs of certain sites [1])
A lighthouse acts as a navigation aid to ships at sea in a manner that is non-excludable.
An excludable good could be a magazine; people who do not pay for the subscription are mostly excluded from obtaining a copy directly from the publisher. Another case in point is a pay television subscription.
