diff --git a/bench.md b/bench.md
index 9d4da53..138f243 100644
--- a/bench.md
+++ b/bench.md
@@ -30,6 +30,8 @@ bench-v8源代码在QuickJS测试档案（`tests/bench-v8`目录）中提供。
 
 在Fedora 21上使用gcc 4.9.2编译所有程序。它们在3.2 GHz的Core i5 4570 CPU上运行。
 
+**可执行文件尺寸**是指运行引擎所需的所有资源(除了系统C库)的大小。
+
 *   [QuickJS](https://bellard.org/quickjs): version 2019-07-09, qjs executable, x86, 64 bits, compiled with -O2.
 *   [DukTape](https://duktape.org/): version 2.3.0, duk executable, x86, 64 bits, compiled with -O2.
 *   [XS](https://github.com/Moddable-OpenSource/moddable): version 8.8.0, xst executable, x86, 64 bits, compiled with -O3. The engine cannot correctly run the RegExp test, so it was disabled.