docs: add glossary terms for statement/connection/database (#1654)

Fixes #1652.

docs/source/cpp/recipe/quickstart.cc

@@ -116,11 +116,11 @@ int main() {
   /// Creating a Connection
   /// ---------------------
   ///
-  /// ADBC distinguishes between "databases", "connections", and
-  /// "statements".  A "database" holds shared state across multiple
-  /// connections.  For example, in the SQLite driver, it holds the
-  /// actual instance of SQLite.  A "connection" is one connection to
-  /// the database.
+  /// ADBC distinguishes between ":term:`databases <database>`",
+  /// ":term:`connections <connection>`", and ":term:`statements
+  /// <statement>`".  A "database" holds shared state across multiple
+  /// connections.  For example, in the SQLite driver, it holds the actual
+  /// instance of SQLite.  A "connection" is one connection to the database.
 
   AdbcConnection connection = {};
   CHECK_ADBC(AdbcConnectionNew(&connection, &error));

docs/source/glossary.rst

@@ -30,6 +30,14 @@ Glossary
      abstract over the underlying :term:`wire protocol` and other details.
      For example, ADBC, JDBC, ODBC.
 
+   connection
+     In ADBC, the connection object/struct represents a single connection to a
+     database.  Multiple connections may be created from one :term:`database`.
+
+   database
+     In ADBC, the database object/struct holds state that is shared across
+     connections.
+
    driver
      Loosely speaking, a library that implements a :term:`client API` using a
      :term:`wire protocol`.  For example, the ADBC PostgreSQL driver exposes
@@ -48,6 +56,12 @@ Glossary
      would collide otherwise.)  In Python, it loads drivers and provides
      Python bindings on top.
 
+   statement
+     In ADBC, the statement object/struct holds state for executing a single
+     query.  The query itself, bind parameters, result sets, and so on are all
+     tied to the statement.  Multiple statements may be created from one
+     :term:`connection` (though not all drivers will support this).
+
    Substrait
      `Substrait`_ describes itself as a "cross-language serialization for
      relational algebra".  It operates in a similar space as SQL, but is