What is a tour?
When chamber music clubs wish to promote concerts by the same ensemble (say, a particular string quartet), they often get together to see if they can coordinate, so that the quartet plays (virtually) the same concert in different venues on successive evenings.
This can be financially advantageous, as not only are the ensemble's travel expenses shared, but their concert fees are reduced for playing the same works on successive evenings.
The main forum for clubs "getting together" is the Tours Conference, held in the Autumn of each year, under the auspices of Enterprise Music Scotland, although clubs may meet at other times.
At these meetings, clubs happily share their wishes, so that tours by these ensembles can be created.