I am relatively new to the term "privilege", but I have many years of experience understanding the ways in which I have privilege and the ways in which I do not have privilege. Privilege is a complicated idea, but I boil it down to access. Most web applications use some form of access rights to determine who can do certain actions. These access rights are also called privileges.
Take Twitter as an example. If you are the owner of a Twitter account, then you have privileges that let you do things like change your password, post on your Twitter feed, protect your tweets, and change your profile and banner images. If you are not the the owner, then you can't do any of those things, but you can retweet the account (if it is not protected) and also tweet a reply (again, if it is not protected). So, both the Twitter account owner and those who don't own the account have different sets of privileges.
Society also presents different sets of privileges based on things none of us choose such as our gender, skin color, or place of origin. These privileges often restrict or impede what we can and what we cannot do. Privilege is the headwind against the flight of freedom.
Over the past two weeks, I have seen several well written articles that use analogies to describe the difficult concept of privilege. One uses the analogy of a bike to explain the experience of not having privilege. There is a Part 1 and a Part 2. The other article uses the analogy of a recycle bin to describe what it's like to have privilege. Both are short reads and worth reading.