Definition of barriers:
(n) :
A structure that bars passage.
(n) :
An obstacle or impediment.
(n) :
A boundary or limit.
(v) :
(transitive) To block or obstruct with a barrier.
(n) :
(physiology) A separation between two areas of the body where specialized cells allow the entry of certain substances but prevent the entry of others.
(n) :
(grammar) A node (in government and binding theory) said to intervene between other nodes A and B if it is a potential governor for B, c-commands B, and does not c-command A.