Those are types of ads where the target ad URL opens inside a timer and the member is credited after
the counter runs down.
Ad types include PTC, PTR and PTS.
PTC ("paid to click") are clickable ads usually in the form of banners or text links that once clicked opens the target URL inside the timer. This is the most basic form of GPT ad.
PTR ("paid to read") are much like PTC ads but are sent individually to members via email. A PTR ad is usually formed by a text message containing a clickable link (the PTR link).
PTS ("paid to surf") ads are presented in sequence to the user, so when the counter runs down another PTS ad is loaded. Contrary to PTC and PTR, when the counter runs down, a simple CAPTCHA is presented to the user to inhibit automatic navigation.