# What are skew arithmetic circuits?

I am trying to understand the definition of skewed circuits in these slides which is given as follows:

A circuit is skew if in each product gate, at least one product has degree $$\le 1$$.

I think author wants to say that each product gate is either a leaf node or one level above the leaf node.

Another interpretation would be that one of the inputs of any multiplication gate is a linear function of the inputs, that is, it is semantically linear. For example, $$(a+b)^2-(a-b)^2$$ is semantically linear but not syntactically linear. This is probably not the interpretation which is meant here.