1) hypertext: is a text which is not sequential.but organized in such a way so that the reader might discover himself the action of the story,it is an interactive programme allowing the reader to move from one document to another by accessing the links.in some cases it includes also sounds,graphics and videos.
 http://www.bennetyee.org//http_webster.cgi?hypertext&method=exact

2) the link is the connection between two separate files or web pages.
http://www.bennetyee.org/http_webster.cgi?link&method=exact

3) lexia: is a block of hypertext connected to another lexia (by links) which communicate with each other,it is the basic block of the hypertextual universe seen nonsequentially yfrom the point of  view of the author and sequentially from the point of view of the reader.
http://www.magnesium.net/~gregsamsa/lexiacon/archives/000001.html

4) the node is a host machine on the network.,an interconnection point on a computer network.
http://www.wordreference.com/english/definition.asp?en=node