Web, domains and email
URI
Abbreviation for Uniform Resource Identifier
In short and in plain language
A URI is a string of characters. It names something on the internet.
That can be a web page, a file or an email address.
A web address is one kind of it. It also says where to fetch the thing.
Definition
A URI is a string of characters that uniquely identifies a resource on the internet, such as a web page, file or email address. A URL is a kind of URI that also states where and how the resource can be retrieved.