1. Credit line sharing under the Bank of Communications credit card means that the credit lines of the subsidiary card and the main card of the Bank of Communications credit card are shared, that is, the two cards share one credit line.

2. The so-called "shared line" means that all credit cards held by the same cardholder use a common line. For example, if you hold five credit cards of a bank with a credit line of 10000 yuan, then the shared credit line of these five credit cards is 10000 yuan. When you overdraw 2000 yuan with one card, you can also overdraw 8000 yuan with the other four cards.

3. Extended explanation: Credit line sharing means that credit cards of the same bank and brand share the same credit line (generally the highest credit line for one card). Although several cards have their own credit limits, the total overdraft in use cannot exceed the shared credit limit of the brand credit card.