GPT site means Get Paid To .. site. A GPT site offers members to be paid to make different actions on websites and less frequently offline - phone calls for instance.
Most frequent paid actions are:
filling out webforms
According to their nature, actions are commonly paid within a range from $0.05 to $1. There are often contests with money prizes for members completing the larger number of actions.
The GPT sites are theoritically paid by commissions from affiliate merchant but this type of site is often banished from affiliate programs because their provided leads don’t convert - people fill forms for money and not because they are interested in a product or service.
The real business model behind GPT site may be paid services offered to members - for more details about the model perversion see PTC site definition.
It exists more than 100 GPT sites on US language market and few dedicated companies probably own several of them.
Some sites are a mix of GPT & PTC sites:
Some ads for GPT sites: