EfficientNet function composition or Hadamard
It probably represents repeated function composition.
Key reasons:

The authors' wording before this equation is: &quot;a list of composed layers&quot;.
A Hadamard product could not be applied to layers of different sizes, whereas function composition of course can.
Yes, EfficientNet has skip connections, but I think they try to validate function composition via a distinction between &quot;layers&quot; and &quot;stages&quot;. They say that &quot;$F_i^{L_i}$ denotes layer $F_i$ is repeated $L_i$ times in stage $i$&quot;. They also explain that &quot;all layers in each stage share the same architecture. Therefore, I think they put skip-connections in the form of function composition, but it is confusing. I think it's their way of compactly expressing the (often) repeated architecture of skip-connected layers.