The Business Code is a 6 digit number for your activity. Here are the IRS instructions for Schedule C. Business codes start on page 19.
http://www.irs.gov/pub/irs-pdf/i1040sc.pdf
See the FAQ on Business Codes,
https://ttlc.intuit.com/turbotax-support/en-us/help-article/business-taxes/business-code-used/L6QD0x...
