Doc: fix meaning of acronym "btree".

Acronym "btree" better means "multi-way balanced tree" rather than
"multi-way binary tree".

Discussion: https://postgr.es/m/20190105.183532.1686260542006440682.t-ishii%40sraoss.co.jp

diff --git a/doc/src/sgml/btree.sgml b/doc/src/sgml/btree.sgml
index c16825e2eafb98cbf20c3e87fc617207923edbc8..996932e35d0ced4b1b72fe421fadc4c4fc8a0d84 100644 (file)
--- a/doc/src/sgml/btree.sgml
+++ b/doc/src/sgml/btree.sgml
@@ -13,7 +13,7 @@
 
  
   PostgreSQL includes an implementation of the
-  standard btree (multi-way binary tree) index data
+  standard btree (multi-way balanced tree) index data
   structure.  Any data type that can be sorted into a well-defined linear
   order can be indexed by a btree index.  The only limitation is that an
   index entry cannot exceed approximately one-third of a page (after TOAST