In terms of this paper, my understanding is indegree is the amount of papers that cite a given paper and outdegree is the amount of papers that the paper cites. The greater the difference between papers that cite a paper and those a paper cites, the greater its chance of being seen by newer papers.

The quality of a citation is important as well. To assess the quality of a citation, the authors determined that if a paper is cited by other papers that are highly cited, then that citation is of greater value and deserves greater weight.

Reference

Prabhakaran, T., Lathabai, H.H., George, S. et al. Towards prediction of paradigm shifts from scientific literature. Scientometrics 117, 1611–1644 (2018). https://doi.org/10.1007/s11192-018-2931-3