An action is a completed activity by an end-user. This can be a sale where the end-user buys something (pay-per-sale), a signup where the user makes a free account (pay-per-lead), an install where the user installs an application (per per install) or any other number of actions that are used by advertisers to pay publishers.
An advertiser is a party who buys adspace. They pay for traffic and actions.
An impression is each time a an ad is displayed. For example if you go to a website and you see a banner ad, that counts as 1 impression of that ad. If there are 3 banner ads on a webpage, that counts as 3 ad impressions and 1 page view.
A page view measures how many times a page is loaded. Depending on the tracking software, this could be how many times a page request was sent (regardless of whether it’s viewed by a human or not) or when a page is loaded by a browser.
A publisher is a party with content who has adspace available for sale. They get paid for sending traffic and actions. An example would be a news website. It has content in the form of articles which attracts viewers. It can then sell this adspace, for example banners at the top of every page, to others in exchange for money.
Demand Side Platform (DSP)
A demand-side platform (DSP) is a system that allows buyers of digital advertising inventory to manage multiple ad exchange and data exchange accounts through one interface.