What is a semantic gap?

In terms of transfer learning, semantic gap means different meanings and purposes behind the same syntax between two or more domains. For example, suppose that we have a deep learning application to detect and label a sequence of actions/words a1,a2,…,an in a video/text as a "greeting" in a society A. However, this knowledge in Society A cannot be transferred to another society B that the same sequence of actions in that society means "criticising"! Although the example is very abstract, it shows the semantic gap between the two domains. You can see the different meanings behind the same syntax or sequence of actions in two domains: Societies A and B. This phenomenon is called the "semantic gap"