Steam and Dota 2 Friend accounts

The term Steam ID refers to a unique identifier for a specific Steam account. It can be formatted in a few different ways, but the most commonly used is the account's 64 bit ID which is a 17 digit number.

Your can find your SteamID by clicking on 'open my profile' in Steam and then on 'edit profile'. In the section 'General' you will as an url under 'CUSTOM URL'. The number in the URL is your SteamID.