Change "primary rule" to "default rule"
diff --git a/icu4c/source/i18n/unicode/rbnf.h b/icu4c/source/i18n/unicode/rbnf.h
index df7449f..283e969 100644
--- a/icu4c/source/i18n/unicode/rbnf.h
+++ b/icu4c/source/i18n/unicode/rbnf.h
@@ -297,7 +297,7 @@
* </tr>
* <tr>
* <td>x.0:</td>
- * <td>The rule is a <em>primary rule</em>. If the full stop in
+ * <td>The rule is a <em>default rule</em>. If the full stop in
* the middle of the rule name is replaced with the decimal point
* that is used in the language or DecimalFormatSymbols, then that rule will
* have precedence when formatting and parsing this rule. For example, some
@@ -332,9 +332,9 @@
* algorithms: If the rule set is a regular rule set, do the following:
*
* <ul>
- * <li>If the rule set includes a primary rule (and the number was passed in as a <tt>double</tt>),
- * use the primary rule. (If the number being formatted was passed in as a <tt>long</tt>,
- * the primary rule is ignored.)</li>
+ * <li>If the rule set includes a default rule (and the number was passed in as a <tt>double</tt>),
+ * use the default rule. (If the number being formatted was passed in as a <tt>long</tt>,
+ * the default rule is ignored.)</li>
* <li>If the number is negative, use the negative-number rule.</li>
* <li>If the number has a fractional part and is greater than 1, use the improper fraction
* rule.</li>
@@ -393,7 +393,7 @@
* </tr>
* <tr>
* <td></td>
- * <td>in fraction or primary rule</td>
+ * <td>in fraction or default rule</td>
* <td>Isolate the number's fractional part and format it.</td>
* </tr>
* <tr>
@@ -425,7 +425,7 @@
* </tr>
* <tr>
* <td></td>
- * <td>in fraction or primary rule</td>
+ * <td>in fraction or default rule</td>
* <td>Isolate the number's integral part and format it.</td>
* </tr>
* <tr>
@@ -456,7 +456,7 @@
* </tr>
* <tr>
* <td></td>
- * <td>in primary rule</td>
+ * <td>in default rule</td>
* <td>Omit the optional text if the number is an integer (same as specifying both an x.x
* rule and an x.0 rule)</td>
* </tr>
