medium 指按照某种标准来说是适中或中等的。这种标准可以是通过仪器测量而来，也可能是凭经验而得出。
average 通常用来形容优劣难分的平庸或折衷情况，也指理论上的平均标准。
参考例句
1. Television is an important medium of communication. 电视是一种重要的传播媒体。
2. One of my suitcases is small, and the other one is medium size. 我的一个手提箱是小个的，不过另外一个是中号的。
3. Objective: Open the statistics window and use the filter for the following types: battleships, destroyers, medium bombers. 目的：打开统计表窗口和使用过滤器为下列的类型：战舰、驱逐舰，中型轰炸机。
英英解释
n.
1. a means or instrumentality for storing or communicating information
2. the surrounding environment
3. an intervening substance through which signals can travel as a means for communication
4. (bacteriology) a nutrient substance (solid or liquid) that is used to cultivate micro-organisms
5. an intervening substance through which something is achieved
6. a liquid with which pigment is mixed by a painter
7. (biology) a substance in which specimens are preserved or displayed
8. a state that is intermediate between extremes; a middle position
9. someone who serves as an intermediary between the living and the dead
10. (usually plural) transmissions that are disseminated widely to the public
11. an occupation for which you are especially well suited adj.
1. around the middle of a scale of evaluation of physical measures
2. (meat) cooked until there is just a little pink meat inside
