Formal

Formal fallacies are all the cases or kinds of reasoning that fail to be deductively valid. Formal fallacies are also called logical fallacies or invalidities.

Example:

Some cats are tigers. Some tigers are animals. So, some cats are animals.

This might at first seem to be a good argument, but actually it is fallacious because it has the same logical form as the following more obviously invalid argument:

Some women are Americans. Some Americans are men. So, some women are men.

Nearly all the infinity of types of invalid inferences have no specific fallacy names.