od6 is the worksheet-id of the 'default' sheet within your Google Spreadsheet. That is, the leftmost sheet visible within the interface.

Ask for your worksheet feed by going to:

https://spreadsheets.google.com/feeds/worksheets/YOURSPREADSHEETID/private/full

Google Sheets API for accessing spreadsheet feed in JSON format.

https://spreadsheets.google.com/feeds/list/YOURSPREADSHEETID/od3otrm/public/values?alt=json

Reference:-

• Sheets API https://developers.google.com/google-apps/spreadsheets/worksheets?hl=en

• od6 and Finding Other Worksheet IDs