I'm super new to deep learning and computer vision, so this question may sound dumb.
In this link (https://github.com/GeorgeSeif/Semantic-Segmentation-Suite), there are pre-trained models (e.g., ResNet101) called front-end models. And they are used for feature extraction. I found these models are called backbone models/architectures generally. And the link says some of the main models (e.g. DeepLabV3 or PSPNet) rely on pre-trained ResNet.
Also, transfer learning is to take a model trained on a large dataset and transfer its knowledge to a smaller dataset, right?
Do the main models that rely on pre-trained ResNet do transfer learning basically (like from ResNet to the main model)?
If I use a pre-trained network, like ResNet101, as the backbone architecture of the main model(like U-Net or SegNet) for image segmentation, is it considered as transfer learning?