The GA travel card is a pass that allows unlimited travel on all public transport. It is usually bought for a whole year and targeted to local commuters.
The Swiss Travel Pass, and Swiss Travel Pass Flex are products aimed at tourists, and they also offer unlimited travel on all public transit. The Flex pass is in my opinion not very useful though. Either get the STS, or get the Half Fare Card, and just buy tickets and/or day passes.
Often you will see the area where unlimited public transport passes are valid in referred to as the “GA Travel Area”. So maybe that is the source of your confusion.