1. On p.67 Tseng means the [Tensor product of representations](https://en.wikipedia.org/wiki/Tensor_product_of_representations).

2. On  p.70 Tseng means the [direct product of groups](https://en.wikipedia.org/wiki/Direct_product_of_groups). Note however that the actual statement about the Lorentz group is wrong/imprecise as explained in e.g. [this](https://physics.stackexchange.com/q/28505/2451) Phys.SE post. 

3. See also my related Phys.SE answer [here](https://physics.stackexchange.com/a/99305/2451).