Ramsar sites take their name from the location of the first meeting of the Convention on Wetlands of International Importance which was held in Ramsar, Iran in 1971.  The designation is attributed to wetland sites of international importance.  Originally this primarily focused on sites that were of international importance to birds but the scope of the designation has now been extended and recognises wetlands as an ecosystem that are extremely important for biodiversity conservation in general and for the well-being of human communities.
As a result the designation is one of the few that affords protection to the whole community or ecosystem rather than specific species.  The Convention requires governments protect wetlands and encourage the wise use of wetland areas.

The first UK Ramsar site was designated in 1976 and there are now 146 recognised within the UK  The UK has a fairly high proportion of the total international sites designated although they tend to be over a smaller area then some countries.

More information on Ramsar sites can be found on the JNCC website.