In Google Sheets, Spreadsheet ID is an identifier that’s unique to a Spreadsheet.
This ID is the value between the "/d/" and the "/edit" in the URL of your spreadsheet. For example, consider the following URL that references a Google Sheets spreadsheet:
https://docs.google.com/spreadsheets/d/1Vq2Q9FIBj_ut7ZMLwX1Vq2Q9FIBj_ut7ZMLwX-hpjd/edit#gid=0The ID of this spreadsheet is 1Vq2Q9FIBj_ut7ZMLwX1Vq2Q9FIBj_ut7ZMLwX-hpjd.