What does "low ethylene" apple cultivar mean?

Ethylene is a small gaseous molecule which is present in all plant tissues.  Interestingly, it is a plant hormone and is actively involved in many physiological processes.  One very important process in apples in which ethylene is intimately involved is ripening.  Specifically, ethylene is the triggering molecule for apple ripening.  If ethylene is removed from the fruit or its production is limited within the fruit, ripening will be slowed or, in some cases, nearly stopped.  Low-ethylene cultivars have an inherently lower production of ethylene than do standard cultivars.  This often will effect ripening rate and potentially storability.