Your resale license (and corresponding number) is issued by your state or local municipality. As the name implies, it entitles you to purchase products at wholesale prices and re-sell them. Your resale license also provides sales tax exemption on your wholesale purchases. The license proves to a wholesaler that you're using their goods and products in the manufacture of your final product, and that you will collect the sales tax from the end users.
Your state or local government issues resale licenses to ensure that you are authorized to collect sales tax on taxable products. Moreover, it is used to track your payments of sales tax to the proper tax body. Different municipalities have different names for the resale license. They include Seller's Permit, Use and Sales Tax License, Transaction Privilege Tax, Application to Collect/Report Tax, and Resale Certificate. They all serve the same purpose.
Tax ID Number
Your tax identification number is the one specifically set aside for income tax reporting purposes to the IRS and your state and local authorities. It is used by most companies to report earnings and taxes for state, federal, workman's compensation, etc. Known as an EIN (Employer Identification Number), you may be required to obtain one from the federal government, as well as from your state government, depending on the size of your business. This number is different from your resale number.