Here are a few options for a WordPress post_tag description for “線上交易” in Traditional Chinese, ranging in formality and specificity:

**Option 1: General & Simple**

* **Description:** 關於網上買賣活動。
* **Translation:** About online buying and selling activities.
* **Target Audience:** Broad audience.

**Option 2: Slightly More Specific**

* **Description:** 所有透過互聯網進行的交易，包括購物、支付等。
* **Translation:** All transactions conducted via the internet, including shopping, payments, etc.
* **Target Audience:** People interested in understanding the breadth of online transactions.

**Option 3: Focusing on Security (If relevant to your content)**

* **Description:** 關注網上交易安全及相關資訊，確保交易順利進行。
* **Translation:** Focusing on online transaction security and relevant information, ensuring smooth transactions.
* **Target Audience:** Focused on users worried or curious about the safety aspect.

**Option 4: More Comprehensive & Keyword-Rich (For SEO)**

* **Description:** 包括網上購物、電子支付、股票交易、外匯買賣等各類線上買賣活動。 提供最新交易資訊、安全提示、及相關教學。
* **Translation:** Includes online shopping, electronic payments, stock trading, foreign exchange transactions and other types of online buying and selling activities. Offers the latest transaction information, security tips, and related tutorials.
* **Target Audience:** Aims to attract users with a wider search range related to online transactions.

**Choosing the best option:**

Consider these factors when choosing:

* **The core content of your posts tagged with “線上交易”:** What topics do you cover most frequently?
* **Your target audience:** Who are you trying to reach?
* **Your SEO goals:** Do you want to rank for specific keywords?

You can also customize these options further to fit your specific needs. Remember to use Traditional Chinese characters correctly. Choose the description that best reflects the content tagged with “線上交易” on your website.