备用信用证的定义和前述信用证的定义并无不同，都是银行（开证行）应申请人的请求，向受益人开立的，在一定条件下凭规定的单据向受益人支付一定款项的书面凭证。所不同的是，规定的单据不同。备用信用证要求受益人提交的单据，不是货运单据，而是受益人出具的关于申请人违约的声明或证明。
传统的银行保函有可能使银行卷入商业纠纷，美、日等国的法律禁止银行开立保函。于是美国银行采用备用信用证的形式，对国际经济交易行为提供担保。随着银行保函在应用中性质的变化，特别是1992年国际商会《见索即付保函统一规则》的公布，银行保函和备用信用证的内容和作用已趋一致。所不同的只是两者遵循的惯例不同。备用信用证运用于“UCP 500”，而银行保函则适用于上述《规则》。
备用信用证是担保银行向贴现或贷款银行承诺到期为借款方偿还债务，如果借款方到期偿还了贷款，那么，备用信用证就备而不用，如果，借款方到期不归还贷款，那么，备用信用证就起作用，担保银行就要为借款方向贷款银行偿还贷款。备用信用证有无条件兑付信用证和有条件兑付信用证。
备用信用证本：
To: Bank of communications, SHENYING Branch
With reference to the loan agreement no. 2004HN028 (hereinafter referred to as "the agreement" ) signed between Bank of Communications, SHENYANG Branch (hereinafter referred to as "the lender" ) and LIAONING ABC CO., LTD (hereinafter referred to as "the borrower" )for a principal amount of RMB2,000,000 (in words),we hereby issue our irrevocable standby letter of credit no.810LC040000027D in the lender's favor for amount of the HONGKONG AABBCC CORPORATION which has its registered office at AS 8 FL. 2SEC. CHARACTER RD. HONG KONG for an amount up to UNITED STATES DOLLARS THREE MILLION ONLY.(USD3,000,000) which covers the principal amount of the agreement plus interest accrued from aforesaid principal amount and other charges all of which the borrower has undertaken to pay the lender. The exchange rate will be the buying rate of USD/RMB quoted by Bank of Communications on the date of our payment. In the case that the guaranteed amount is not sufficient to satisfy your claim due to the exchange rate fluctuation between USD and RMB we hereby agree to increase the amount of this standby L/C accordingly.
Partial drawing and multiple drawing are allowed under this standby L/C.
This standby letter of credit is available by sight payment. We engage with you that upon receipt of your draft(s) and your signed statement or tested telex statement or SWIFT stating that the amount in USD represents the unpaid balance of indebtedness due to you by the borrower, we will pay you within 7 banking days the amount specified in your statement or SWIFT. All drafts drawn hereunder must be marked drawn under XYZ Bank standby letter of credit no. 810LC040000027D dated 20 DECEMBER 2004.
This standby letter of is credit will come into effect on 20 DECEMBER 2004 and expire on 09 DECEMBER 2005 at the counter of bank of Communications , SHENYANG branch.
This standby letter of credit is subject to Uniform Customs and Practice for Document Credits(1993 revision) International Chamber of Commerce Publication No.500.
