As a noun, scale refers to the relative size of an object. For instance, to say "the scale of the project was enormous," indicates that other projects are less complex, or less ambitious in scope.
As a verb, "to scale" means to make something larger or smaller compared to its previous size. In computers, scaled objects include visual objects such as images or fonts, or abstract objects such as data or file size. An image can be scaled using an image editor, for example.
Scaling on the web
The ability of web applications to "scale well" has been revolutionized by cloud computing and virtual machines. These technologies enable web server resources, such as bandwidth, CPUs, RAM, and disk space, to be allocated and cloned at the click of a button. Cloud services such as AWS, GCP, and Azure have simplified scaling websites on demand.
To perform web development or operational duties at scale means to work with systems capable of serving a massive or rapidly growing number of users.